luci-base: luci.js: allow overriding response type for requests

[project/luci.git] / modules / luci-base / htdocs / luci-static / resources / luci.js

/**
 * @class LuCI
 * @classdesc
 *
 * This is the LuCI base class. It is automatically instantiated and
 * accessible using the global `L` variable.
 *
 * @param {Object} env
 * The environment settings to use for the LuCI runtime.
 */

(function(window, document, undefined) {
        'use strict';

        /* Object.assign polyfill for IE */
        if (typeof Object.assign !== 'function') {
                Object.defineProperty(Object, 'assign', {
                        value: function assign(target, varArgs) {
                                if (target == null)
                                        throw new TypeError('Cannot convert undefined or null to object');

                                var to = Object(target);

                                for (var index = 1; index < arguments.length; index++)
                                        if (arguments[index] != null)
                                                for (var nextKey in arguments[index])
                                                        if (Object.prototype.hasOwnProperty.call(arguments[index], nextKey))
                                                                to[nextKey] = arguments[index][nextKey];

                                return to;
                        },
                        writable: true,
                        configurable: true
                });
        }

        /* Promise.finally polyfill */
        if (typeof Promise.prototype.finally !== 'function') {
                Promise.prototype.finally = function(fn) {
                        var onFinally = function(cb) {
                                return Promise.resolve(fn.call(this)).then(cb);
                        };

                        return this.then(
                                function(result) { return onFinally.call(this, function() { return result }) },
                                function(reason) { return onFinally.call(this, function() { return Promise.reject(reason) }) }
                        );
                };
        }

        /*
         * Class declaration and inheritance helper
         */

        var toCamelCase = function(s) {
                return s.replace(/(?:^|[\. -])(.)/g, function(m0, m1) { return m1.toUpperCase() });
        };

        /**
         * @class Class
         * @hideconstructor
         * @memberof LuCI
         * @classdesc
         *
         * `LuCI.Class` is the abstract base class all LuCI classes inherit from.
         *
         * It provides simple means to create subclasses of given classes and
         * implements prototypal inheritance.
         */
        var superContext = {}, classIndex = 0, Class = Object.assign(function() {}, {
                /**
                 * Extends this base class with the properties described in
                 * `properties` and returns a new subclassed Class instance
                 *
                 * @memberof LuCI.Class
                 *
                 * @param {Object<string, *>} properties
                 * An object describing the properties to add to the new
                 * subclass.
                 *
                 * @returns {LuCI.Class}
                 * Returns a new LuCI.Class sublassed from this class, extended
                 * by the given properties and with its prototype set to this base
                 * class to enable inheritance. The resulting value represents a
                 * class constructor and can be instantiated with `new`.
                 */
                extend: function(properties) {
                        var props = {
                                __id__: { value: classIndex },
                                __base__: { value: this.prototype },
                                __name__: { value: properties.__name__ || 'anonymous' + classIndex++ }
                        };

                        var ClassConstructor = function() {
                                if (!(this instanceof ClassConstructor))
                                        throw new TypeError('Constructor must not be called without "new"');

                                if (Object.getPrototypeOf(this).hasOwnProperty('__init__')) {
                                        if (typeof(this.__init__) != 'function')
                                                throw new TypeError('Class __init__ member is not a function');

                                        this.__init__.apply(this, arguments)
                                }
                                else {
                                        this.super('__init__', arguments);
                                }
                        };

                        for (var key in properties)
                                if (!props[key] && properties.hasOwnProperty(key))
                                        props[key] = { value: properties[key], writable: true };

                        ClassConstructor.prototype = Object.create(this.prototype, props);
                        ClassConstructor.prototype.constructor = ClassConstructor;
                        Object.assign(ClassConstructor, this);
                        ClassConstructor.displayName = toCamelCase(props.__name__.value + 'Class');

                        return ClassConstructor;
                },

                /**
                 * Extends this base class with the properties described in
                 * `properties`, instantiates the resulting subclass using
                 * the additional optional arguments passed to this function
                 * and returns the resulting subclassed Class instance.
                 *
                 * This function serves as a convenience shortcut for
                 * {@link LuCI.Class.extend Class.extend()} and subsequent
                 * `new`.
                 *
                 * @memberof LuCI.Class
                 *
                 * @param {Object<string, *>} properties
                 * An object describing the properties to add to the new
                 * subclass.
                 *
                 * @param {...*} [new_args]
                 * Specifies arguments to be passed to the subclass constructor
                 * as-is in order to instantiate the new subclass.
                 *
                 * @returns {LuCI.Class}
                 * Returns a new LuCI.Class instance extended by the given
                 * properties with its prototype set to this base class to
                 * enable inheritance.
                 */
                singleton: function(properties /*, ... */) {
                        return Class.extend(properties)
                                .instantiate(Class.prototype.varargs(arguments, 1));
                },

                /**
                 * Calls the class constructor using `new` with the given argument
                 * array being passed as variadic parameters to the constructor.
                 *
                 * @memberof LuCI.Class
                 *
                 * @param {Array<*>} params
                 * An array of arbitrary values which will be passed as arguments
                 * to the constructor function.
                 *
                 * @param {...*} [new_args]
                 * Specifies arguments to be passed to the subclass constructor
                 * as-is in order to instantiate the new subclass.
                 *
                 * @returns {LuCI.Class}
                 * Returns a new LuCI.Class instance extended by the given
                 * properties with its prototype set to this base class to
                 * enable inheritance.
                 */
                instantiate: function(args) {
                        return new (Function.prototype.bind.apply(this,
                                Class.prototype.varargs(args, 0, null)))();
                },

                /* unused */
                call: function(self, method) {
                        if (typeof(this.prototype[method]) != 'function')
                                throw new ReferenceError(method + ' is not defined in class');

                        return this.prototype[method].apply(self, self.varargs(arguments, 1));
                },

                /**
                 * Checks whether the given class value is a subclass of this class.
                 *
                 * @memberof LuCI.Class
                 *
                 * @param {LuCI.Class} classValue
                 * The class object to test.
                 *
                 * @returns {boolean}
                 * Returns `true` when the given `classValue` is a subclass of this
                 * class or `false` if the given value is not a valid class or not
                 * a subclass of this class'.
                 */
                isSubclass: function(classValue) {
                        return (classValue != null &&
                                typeof(classValue) == 'function' &&
                                classValue.prototype instanceof this);
                },

                prototype: {
                        /**
                         * Extract all values from the given argument array beginning from
                         * `offset` and prepend any further given optional parameters to
                         * the beginning of the resulting array copy.
                         *
                         * @memberof LuCI.Class
                         * @instance
                         *
                         * @param {Array<*>} args
                         * The array to extract the values from.
                         *
                         * @param {number} offset
                         * The offset from which to extract the values. An offset of `0`
                         * would copy all values till the end.
                         *
                         * @param {...*} [extra_args]
                         * Extra arguments to add to prepend to the resultung array.
                         *
                         * @returns {Array<*>}
                         * Returns a new array consisting of the optional extra arguments
                         * and the values extracted from the `args` array beginning with
                         * `offset`.
                         */
                        varargs: function(args, offset /*, ... */) {
                                return Array.prototype.slice.call(arguments, 2)
                                        .concat(Array.prototype.slice.call(args, offset));
                        },

                        /**
                         * Walks up the parent class chain and looks for a class member
                         * called `key` in any of the parent classes this class inherits
                         * from. Returns the member value of the superclass or calls the
                         * member as function and returns its return value when the
                         * optional `callArgs` array is given.
                         *
                         * This function has two signatures and is sensitive to the
                         * amount of arguments passed to it:
                         *  - `super('key')` -
                         *    Returns the value of `key` when found within one of the
                         *    parent classes.
                         *  - `super('key', ['arg1', 'arg2'])` -
                         *    Calls the `key()` method with parameters `arg1` and `arg2`
                         *    when found within one of the parent classes.
                         *
                         * @memberof LuCI.Class
                         * @instance
                         *
                         * @param {string} key
                         * The name of the superclass member to retrieve.
                         *
                         * @param {Array<*>} [callArgs]
                         * An optional array of function call parameters to use. When
                         * this parameter is specified, the found member value is called
                         * as function using the values of this array as arguments.
                         *
                         * @throws {ReferenceError}
                         * Throws a `ReferenceError` when `callArgs` are specified and
                         * the found member named by `key` is not a function value.
                         *
                         * @returns {*|null}
                         * Returns the value of the found member or the return value of
                         * the call to the found method. Returns `null` when no member
                         * was found in the parent class chain or when the call to the
                         * superclass method returned `null`.
                         */
                        super: function(key, callArgs) {
                                if (key == null)
                                        return null;

                                var slotIdx = this.__id__ + '.' + key,
                                    symStack = superContext[slotIdx],
                                    protoCtx = null;

                                for (protoCtx = Object.getPrototypeOf(symStack ? symStack[0] : Object.getPrototypeOf(this));
                                     protoCtx != null && !protoCtx.hasOwnProperty(key);
                                     protoCtx = Object.getPrototypeOf(protoCtx)) {}

                                if (protoCtx == null)
                                        return null;

                                var res = protoCtx[key];

                                if (arguments.length > 1) {
                                        if (typeof(res) != 'function')
                                                throw new ReferenceError(key + ' is not a function in base class');

                                        if (typeof(callArgs) != 'object')
                                                callArgs = this.varargs(arguments, 1);

                                        if (symStack)
                                                symStack.unshift(protoCtx);
                                        else
                                                superContext[slotIdx] = [ protoCtx ];

                                        res = res.apply(this, callArgs);

                                        if (symStack && symStack.length > 1)
                                                symStack.shift(protoCtx);
                                        else
                                                delete superContext[slotIdx];
                                }

                                return res;
                        },

                        /**
                         * Returns a string representation of this class.
                         *
                         * @returns {string}
                         * Returns a string representation of this class containing the
                         * constructor functions `displayName` and describing the class
                         * members and their respective types.
                         */
                        toString: function() {
                                var s = '[' + this.constructor.displayName + ']', f = true;
                                for (var k in this) {
                                        if (this.hasOwnProperty(k)) {
                                                s += (f ? ' {\n' : '') + '  ' + k + ': ' + typeof(this[k]) + '\n';
                                                f = false;
                                        }
                                }
                                return s + (f ? '' : '}');
                        }
                }
        });


        /**
         * @class
         * @memberof LuCI
         * @hideconstructor
         * @classdesc
         *
         * The `Headers` class is an internal utility class exposed in HTTP
         * response objects using the `response.headers` property.
         */
        var Headers = Class.extend(/** @lends LuCI.Headers.prototype */ {
                __name__: 'LuCI.XHR.Headers',
                __init__: function(xhr) {
                        var hdrs = this.headers = {};
                        xhr.getAllResponseHeaders().split(/\r\n/).forEach(function(line) {
                                var m = /^([^:]+):(.*)$/.exec(line);
                                if (m != null)
                                        hdrs[m[1].trim().toLowerCase()] = m[2].trim();
                        });
                },

                /**
                 * Checks whether the given header name is present.
                 * Note: Header-Names are case-insensitive.
                 *
                 * @instance
                 * @memberof LuCI.Headers
                 * @param {string} name
                 * The header name to check
                 *
                 * @returns {boolean}
                 * Returns `true` if the header name is present, `false` otherwise
                 */
                has: function(name) {
                        return this.headers.hasOwnProperty(String(name).toLowerCase());
                },

                /**
                 * Returns the value of the given header name.
                 * Note: Header-Names are case-insensitive.
                 *
                 * @instance
                 * @memberof LuCI.Headers
                 * @param {string} name
                 * The header name to read
                 *
                 * @returns {string|null}
                 * The value of the given header name or `null` if the header isn't present.
                 */
                get: function(name) {
                        var key = String(name).toLowerCase();
                        return this.headers.hasOwnProperty(key) ? this.headers[key] : null;
                }
        });

        /**
         * @class
         * @memberof LuCI
         * @hideconstructor
         * @classdesc
         *
         * The `Response` class is an internal utility class representing HTTP responses.
         */
        var Response = Class.extend({
                __name__: 'LuCI.XHR.Response',
                __init__: function(xhr, url, duration, headers, content) {
                        /**
                         * Describes whether the response is successful (status codes `200..299`) or not
                         * @instance
                         * @memberof LuCI.Response
                         * @name ok
                         * @type {boolean}
                         */
                        this.ok = (xhr.status >= 200 && xhr.status <= 299);

                        /**
                         * The numeric HTTP status code of the response
                         * @instance
                         * @memberof LuCI.Response
                         * @name status
                         * @type {number}
                         */
                        this.status = xhr.status;

                        /**
                         * The HTTP status description message of the response
                         * @instance
                         * @memberof LuCI.Response
                         * @name statusText
                         * @type {string}
                         */
                        this.statusText = xhr.statusText;

                        /**
                         * The HTTP headers of the response
                         * @instance
                         * @memberof LuCI.Response
                         * @name headers
                         * @type {LuCI.Headers}
                         */
                        this.headers = (headers != null) ? headers : new Headers(xhr);

                        /**
                         * The total duration of the HTTP request in milliseconds
                         * @instance
                         * @memberof LuCI.Response
                         * @name duration
                         * @type {number}
                         */
                        this.duration = duration;

                        /**
                         * The final URL of the request, i.e. after following redirects.
                         * @instance
                         * @memberof LuCI.Response
                         * @name url
                         * @type {string}
                         */
                        this.url = url;

                        /* privates */
                        this.xhr = xhr;

                        if (content instanceof Blob) {
                                this.responseBlob = content;
                                this.responseJSON = null;
                                this.responseText = null;
                        }
                        else if (content != null && typeof(content) == 'object') {
                                this.responseBlob = null;
                                this.responseJSON = content;
                                this.responseText = null;
                        }
                        else if (content != null) {
                                this.responseBlob = null;
                                this.responseJSON = null;
                                this.responseText = String(content);
                        }
                        else {
                                this.responseJSON = null;

                                if (xhr.responseType == 'blob') {
                                        this.responseBlob = xhr.response;
                                        this.responseText = null;
                                }
                                else {
                                        this.responseBlob = null;
                                        this.responseText = xhr.responseText;
                                }
                        }
                },

                /**
                 * Clones the given response object, optionally overriding the content
                 * of the cloned instance.
                 *
                 * @instance
                 * @memberof LuCI.Response
                 * @param {*} [content]
                 * Override the content of the cloned response. Object values will be
                 * treated as JSON response data, all other types will be converted
                 * using `String()` and treated as response text.
                 *
                 * @returns {LuCI.Response}
                 * The cloned `Response` instance.
                 */
                clone: function(content) {
                        var copy = new Response(this.xhr, this.url, this.duration, this.headers, content);

                        copy.ok = this.ok;
                        copy.status = this.status;
                        copy.statusText = this.statusText;

                        return copy;
                },

                /**
                 * Access the response content as JSON data.
                 *
                 * @instance
                 * @memberof LuCI.Response
                 * @throws {SyntaxError}
                 * Throws `SyntaxError` if the content isn't valid JSON.
                 *
                 * @returns {*}
                 * The parsed JSON data.
                 */
                json: function() {
                        if (this.responseJSON == null)
                                this.responseJSON = JSON.parse(this.responseText);

                        return this.responseJSON;
                },

                /**
                 * Access the response content as string.
                 *
                 * @instance
                 * @memberof LuCI.Response
                 * @returns {string}
                 * The response content.
                 */
                text: function() {
                        if (this.responseText == null && this.responseJSON != null)
                                this.responseText = JSON.stringify(this.responseJSON);

                        return this.responseText;
                },

                /**
                 * Access the response content as blob.
                 *
                 * @instance
                 * @memberof LuCI.Response
                 * @returns {Blob}
                 * The response content as blob.
                 */
                blob: function() {
                        return this.responseBlob;
                }
        });


        var requestQueue = [];

        function isQueueableRequest(opt) {
                if (!classes.rpc)
                        return false;

                if (opt.method != 'POST' || typeof(opt.content) != 'object')
                        return false;

                if (opt.nobatch === true)
                        return false;

                var rpcBaseURL = Request.expandURL(classes.rpc.getBaseURL());

                return (rpcBaseURL != null && opt.url.indexOf(rpcBaseURL) == 0);
        }

        function flushRequestQueue() {
                if (!requestQueue.length)
                        return;

                var reqopt = Object.assign({}, requestQueue[0][0], { content: [], nobatch: true }),
                    batch = [];

                for (var i = 0; i < requestQueue.length; i++) {
                        batch[i] = requestQueue[i];
                        reqopt.content[i] = batch[i][0].content;
                }

                requestQueue.length = 0;

                Request.request(rpcBaseURL, reqopt).then(function(reply) {
                        var json = null, req = null;

                        try { json = reply.json() }
                        catch(e) { }

                        while ((req = batch.shift()) != null)
                                if (Array.isArray(json) && json.length)
                                        req[2].call(reqopt, reply.clone(json.shift()));
                                else
                                        req[1].call(reqopt, new Error('No related RPC reply'));
                }).catch(function(error) {
                        var req = null;

                        while ((req = batch.shift()) != null)
                                req[1].call(reqopt, error);
                });
        }

        /**
         * @class
         * @memberof LuCI
         * @hideconstructor
         * @classdesc
         *
         * The `Request` class allows initiating HTTP requests and provides utilities
         * for dealing with responses.
         */
        var Request = Class.singleton(/** @lends LuCI.Request.prototype */ {
                __name__: 'LuCI.Request',

                interceptors: [],

                /**
                 * Turn the given relative URL into an absolute URL if necessary.
                 *
                 * @instance
                 * @memberof LuCI.Request
                 * @param {string} url
                 * The URL to convert.
                 *
                 * @returns {string}
                 * The absolute URL derived from the given one, or the original URL
                 * if it already was absolute.
                 */
                expandURL: function(url) {
                        if (!/^(?:[^/]+:)?\/\//.test(url))
                                url = location.protocol + '//' + location.host + url;

                        return url;
                },

                /**
                 * @typedef {Object} RequestOptions
                 * @memberof LuCI.Request
                 *
                 * @property {string} [method=GET]
                 * The HTTP method to use, e.g. `GET` or `POST`.
                 *
                 * @property {Object<string, Object|string>} [query]
                 * Query string data to append to the URL. Non-string values of the
                 * given object will be converted to JSON.
                 *
                 * @property {boolean} [cache=false]
                 * Specifies whether the HTTP response may be retrieved from cache.
                 *
                 * @property {string} [username]
                 * Provides a username for HTTP basic authentication.
                 *
                 * @property {string} [password]
                 * Provides a password for HTTP basic authentication.
                 *
                 * @property {number} [timeout]
                 * Specifies the request timeout in seconds.
                 *
                 * @property {boolean} [credentials=false]
                 * Whether to include credentials such as cookies in the request.
                 *
                 * @property {string} [responseType=text]
                 * Overrides the request response type. Valid values or `text` to
                 * interpret the response as UTF-8 string or `blob` to handle the
                 * response as binary `Blob` data.
                 *
                 * @property {*} [content]
                 * Specifies the HTTP message body to send along with the request.
                 * If the value is a function, it is invoked and the return value
                 * used as content, if it is a FormData instance, it is used as-is,
                 * if it is an object, it will be converted to JSON, in all other
                 * cases it is converted to a string.
                 *
             * @property {Object<string, string>} [header]
             * Specifies HTTP headers to set for the request.
             *
             * @property {function} [progress]
             * An optional request callback function which receives ProgressEvent
             * instances as sole argument during the HTTP request transfer.
                 */

                /**
                 * Initiate an HTTP request to the given target.
                 *
                 * @instance
                 * @memberof LuCI.Request
                 * @param {string} target
                 * The URL to request.
                 *
                 * @param {LuCI.Request.RequestOptions} [options]
                 * Additional options to configure the request.
                 *
                 * @returns {Promise<LuCI.Response>}
                 * The resulting HTTP response.
                 */
                request: function(target, options) {
                        var state = { xhr: new XMLHttpRequest(), url: this.expandURL(target), start: Date.now() },
                            opt = Object.assign({}, options, state),
                            content = null,
                            contenttype = null,
                            callback = this.handleReadyStateChange;

                        return new Promise(function(resolveFn, rejectFn) {
                                opt.xhr.onreadystatechange = callback.bind(opt, resolveFn, rejectFn);
                                opt.method = String(opt.method || 'GET').toUpperCase();

                                if ('query' in opt) {
                                        var q = (opt.query != null) ? Object.keys(opt.query).map(function(k) {
                                                if (opt.query[k] != null) {
                                                        var v = (typeof(opt.query[k]) == 'object')
                                                                ? JSON.stringify(opt.query[k])
                                                                : String(opt.query[k]);

                                                        return '%s=%s'.format(encodeURIComponent(k), encodeURIComponent(v));
                                                }
                                                else {
                                                        return encodeURIComponent(k);
                                                }
                                        }).join('&') : '';

                                        if (q !== '') {
                                                switch (opt.method) {
                                                case 'GET':
                                                case 'HEAD':
                                                case 'OPTIONS':
                                                        opt.url += ((/\?/).test(opt.url) ? '&' : '?') + q;
                                                        break;

                                                default:
                                                        if (content == null) {
                                                                content = q;
                                                                contenttype = 'application/x-www-form-urlencoded';
                                                        }
                                                }
                                        }
                                }

                                if (!opt.cache)
                                        opt.url += ((/\?/).test(opt.url) ? '&' : '?') + (new Date()).getTime();

                                if (isQueueableRequest(opt)) {
                                        requestQueue.push([opt, rejectFn, resolveFn]);
                                        requestAnimationFrame(flushRequestQueue);
                                        return;
                                }

                                if ('username' in opt && 'password' in opt)
                                        opt.xhr.open(opt.method, opt.url, true, opt.username, opt.password);
                                else
                                        opt.xhr.open(opt.method, opt.url, true);

                                opt.xhr.responseType = opt.responseType || 'text';

                                if ('overrideMimeType' in opt.xhr)
                                        opt.xhr.overrideMimeType('application/octet-stream');

                                if ('timeout' in opt)
                                        opt.xhr.timeout = +opt.timeout;

                                if ('credentials' in opt)
                                        opt.xhr.withCredentials = !!opt.credentials;

                                if (opt.content != null) {
                                        switch (typeof(opt.content)) {
                                        case 'function':
                                                content = opt.content(xhr);
                                                break;

                                        case 'object':
                                                if (!(opt.content instanceof FormData)) {
                                                        content = JSON.stringify(opt.content);
                                                        contenttype = 'application/json';
                                                }
                                                else {
                                                        content = opt.content;
                                                }
                                                break;

                                        default:
                                                content = String(opt.content);
                                        }
                                }

                                if ('headers' in opt)
                                        for (var header in opt.headers)
                                                if (opt.headers.hasOwnProperty(header)) {
                                                        if (header.toLowerCase() != 'content-type')
                                                                opt.xhr.setRequestHeader(header, opt.headers[header]);
                                                        else
                                                                contenttype = opt.headers[header];
                                                }

                                if ('progress' in opt && 'upload' in opt.xhr)
                                        opt.xhr.upload.addEventListener('progress', opt.progress);

                                if (contenttype != null)
                                        opt.xhr.setRequestHeader('Content-Type', contenttype);

                                try {
                                        opt.xhr.send(content);
                                }
                                catch (e) {
                                        rejectFn.call(opt, e);
                                }
                        });
                },

                handleReadyStateChange: function(resolveFn, rejectFn, ev) {
                        var xhr = this.xhr,
                            duration = Date.now() - this.start;

                        if (xhr.readyState !== 4)
                                return;

                        if (xhr.status === 0 && xhr.statusText === '') {
                                if (duration >= this.timeout)
                                        rejectFn.call(this, new Error('XHR request timed out'));
                                else
                                        rejectFn.call(this, new Error('XHR request aborted by browser'));
                        }
                        else {
                                var response = new Response(
                                        xhr, xhr.responseURL || this.url, duration);

                                Promise.all(Request.interceptors.map(function(fn) { return fn(response) }))
                                        .then(resolveFn.bind(this, response))
                                        .catch(rejectFn.bind(this));
                        }
                },

                /**
                 * Initiate an HTTP GET request to the given target.
                 *
                 * @instance
                 * @memberof LuCI.Request
                 * @param {string} target
                 * The URL to request.
                 *
                 * @param {LuCI.Request.RequestOptions} [options]
                 * Additional options to configure the request.
                 *
                 * @returns {Promise<LuCI.Response>}
                 * The resulting HTTP response.
                 */
                get: function(url, options) {
                        return this.request(url, Object.assign({ method: 'GET' }, options));
                },

                /**
                 * Initiate an HTTP POST request to the given target.
                 *
                 * @instance
                 * @memberof LuCI.Request
                 * @param {string} target
                 * The URL to request.
                 *
                 * @param {*} [data]
                 * The request data to send, see {@link LuCI.Request.RequestOptions} for details.
                 *
                 * @param {LuCI.Request.RequestOptions} [options]
                 * Additional options to configure the request.
                 *
                 * @returns {Promise<LuCI.Response>}
                 * The resulting HTTP response.
                 */
                post: function(url, data, options) {
                        return this.request(url, Object.assign({ method: 'POST', content: data }, options));
                },

                /**
                 * Interceptor functions are invoked whenever an HTTP reply is received, in the order
                 * these functions have been registered.
                 * @callback LuCI.Request.interceptorFn
                 * @param {LuCI.Response} res
                 * The HTTP response object
                 */

                /**
                 * Register an HTTP response interceptor function. Interceptor
                 * functions are useful to perform default actions on incoming HTTP
                 * responses, such as checking for expired authentication or for
                 * implementing request retries before returning a failure.
                 *
                 * @instance
                 * @memberof LuCI.Request
                 * @param {LuCI.Request.interceptorFn} interceptorFn
                 * The interceptor function to register.
                 *
                 * @returns {LuCI.Request.interceptorFn}
                 * The registered function.
                 */
                addInterceptor: function(interceptorFn) {
                        if (typeof(interceptorFn) == 'function')
                                this.interceptors.push(interceptorFn);
                        return interceptorFn;
                },

                /**
                 * Remove an HTTP response interceptor function. The passed function
                 * value must be the very same value that was used to register the
                 * function.
                 *
                 * @instance
                 * @memberof LuCI.Request
                 * @param {LuCI.Request.interceptorFn} interceptorFn
                 * The interceptor function to remove.
                 *
                 * @returns {boolean}
                 * Returns `true` if any function has been removed, else `false`.
                 */
                removeInterceptor: function(interceptorFn) {
                        var oldlen = this.interceptors.length, i = oldlen;
                        while (i--)
                                if (this.interceptors[i] === interceptorFn)
                                        this.interceptors.splice(i, 1);
                        return (this.interceptors.length < oldlen);
                },

                /**
                 * @class
                 * @memberof LuCI.Request
                 * @hideconstructor
                 * @classdesc
                 *
                 * The `Request.poll` class provides some convience wrappers around
                 * {@link LuCI.Poll} mainly to simplify registering repeating HTTP
                 * request calls as polling functions.
                 */
                poll: {
                        /**
                         * The callback function is invoked whenever an HTTP reply to a
                         * polled request is received or when the polled request timed
                         * out.
                         *
                         * @callback LuCI.Request.poll~callbackFn
                         * @param {LuCI.Response} res
                         * The HTTP response object.
                         *
                         * @param {*} data
                         * The response JSON if the response could be parsed as such,
                         * else `null`.
                         *
                         * @param {number} duration
                         * The total duration of the request in milliseconds.
                         */

                        /**
                         * Register a repeating HTTP request with an optional callback
                         * to invoke whenever a response for the request is received.
                         *
                         * @instance
                         * @memberof LuCI.Request.poll
                         * @param {number} interval
                         * The poll interval in seconds.
                         *
                         * @param {string} url
                         * The URL to request on each poll.
                         *
                         * @param {LuCI.Request.RequestOptions} [options]
                         * Additional options to configure the request.
                         *
                         * @param {LuCI.Request.poll~callbackFn} [callback]
                         * {@link LuCI.Request.poll~callbackFn Callback} function to
                         * invoke for each HTTP reply.
                         *
                         * @throws {TypeError}
                         * Throws `TypeError` when an invalid interval was passed.
                         *
                         * @returns {function}
                         * Returns the internally created poll function.
                         */
                        add: function(interval, url, options, callback) {
                                if (isNaN(interval) || interval <= 0)
                                        throw new TypeError('Invalid poll interval');

                                var ival = interval >>> 0,
                                    opts = Object.assign({}, options, { timeout: ival * 1000 - 5 });

                                var fn = function() {
                                        return Request.request(url, options).then(function(res) {
                                                if (!Poll.active())
                                                        return;

                                                try {
                                                        callback(res, res.json(), res.duration);
                                                }
                                                catch (err) {
                                                        callback(res, null, res.duration);
                                                }
                                        });
                                };

                                return (Poll.add(fn, ival) ? fn : null);
                        },

                        /**
                         * Remove a polling request that has been previously added using `add()`.
                         * This function is essentially a wrapper around
                         * {@link LuCI.Poll.remove LuCI.Poll.remove()}.
                         *
                         * @instance
                         * @memberof LuCI.Request.poll
                         * @param {function} entry
                         * The poll function returned by {@link LuCI.Request.poll#add add()}.
                         *
                         * @returns {boolean}
                         * Returns `true` if any function has been removed, else `false`.
                         */
                        remove: function(entry) { return Poll.remove(entry) },

                        /**
                          * Alias for {@link LuCI.Poll.start LuCI.Poll.start()}.
                          *
                          * @instance
                          * @memberof LuCI.Request.poll
                          */
                        start: function() { return Poll.start() },

                        /**
                          * Alias for {@link LuCI.Poll.stop LuCI.Poll.stop()}.
                          *
                          * @instance
                          * @memberof LuCI.Request.poll
                          */
                        stop: function() { return Poll.stop() },

                        /**
                          * Alias for {@link LuCI.Poll.active LuCI.Poll.active()}.
                          *
                          * @instance
                          * @memberof LuCI.Request.poll
                          */
                        active: function() { return Poll.active() }
                }
        });

        /**
         * @class
         * @memberof LuCI
         * @hideconstructor
         * @classdesc
         *
         * The `Poll` class allows registering and unregistering poll actions,
         * as well as starting, stopping and querying the state of the polling
         * loop.
         */
        var Poll = Class.singleton(/** @lends LuCI.Poll.prototype */ {
                __name__: 'LuCI.Poll',

                queue: [],

                /**
                 * Add a new operation to the polling loop. If the polling loop is not
                 * already started at this point, it will be implicitely started.
                 *
                 * @instance
                 * @memberof LuCI.Poll
                 * @param {function} fn
                 * The function to invoke on each poll interval.
                 *
                 * @param {number} interval
                 * The poll interval in seconds.
                 *
                 * @throws {TypeError}
                 * Throws `TypeError` when an invalid interval was passed.
                 *
                 * @returns {boolean}
                 * Returns `true` if the function has been added or `false` if it
                 * already is registered.
                 */
                add: function(fn, interval) {
                        if (interval == null || interval <= 0)
                                interval = window.L ? window.L.env.pollinterval : null;

                        if (isNaN(interval) || typeof(fn) != 'function')
                                throw new TypeError('Invalid argument to LuCI.Poll.add()');

                        for (var i = 0; i < this.queue.length; i++)
                                if (this.queue[i].fn === fn)
                                        return false;

                        var e = {
                                r: true,
                                i: interval >>> 0,
                                fn: fn
                        };

                        this.queue.push(e);

                        if (this.tick != null && !this.active())
                                this.start();

                        return true;
                },

                /**
                 * Remove an operation from the polling loop. If no further operatons
                 * are registered, the polling loop is implicitely stopped.
                 *
                 * @instance
                 * @memberof LuCI.Poll
                 * @param {function} fn
                 * The function to remove.
                 *
                 * @throws {TypeError}
                 * Throws `TypeError` when the given argument isn't a function.
                 *
                 * @returns {boolean}
                 * Returns `true` if the function has been removed or `false` if it
                 * wasn't found.
                 */
                remove: function(fn) {
                        if (typeof(fn) != 'function')
                                throw new TypeError('Invalid argument to LuCI.Poll.remove()');

                        var len = this.queue.length;

                        for (var i = len; i > 0; i--)
                                if (this.queue[i-1].fn === fn)
                                        this.queue.splice(i-1, 1);

                        if (!this.queue.length && this.stop())
                                this.tick = 0;

                        return (this.queue.length != len);
                },

                /**
                 * (Re)start the polling loop. Dispatches a custom `poll-start` event
                 * to the `document` object upon successful start.
                 *
                 * @instance
                 * @memberof LuCI.Poll
                 * @returns {boolean}
                 * Returns `true` if polling has been started (or if no functions
                 * where registered) or `false` when the polling loop already runs.
                 */
                start: function() {
                        if (this.active())
                                return false;

                        this.tick = 0;

                        if (this.queue.length) {
                                this.timer = window.setInterval(this.step, 1000);
                                this.step();
                                document.dispatchEvent(new CustomEvent('poll-start'));
                        }

                        return true;
                },

                /**
                 * Stop the polling loop. Dispatches a custom `poll-stop` event
                 * to the `document` object upon successful stop.
                 *
                 * @instance
                 * @memberof LuCI.Poll
                 * @returns {boolean}
                 * Returns `true` if polling has been stopped or `false` if it din't
                 * run to begin with.
                 */
                stop: function() {
                        if (!this.active())
                                return false;

                        document.dispatchEvent(new CustomEvent('poll-stop'));
                        window.clearInterval(this.timer);
                        delete this.timer;
                        delete this.tick;
                        return true;
                },

                /* private */
                step: function() {
                        for (var i = 0, e = null; (e = Poll.queue[i]) != null; i++) {
                                if ((Poll.tick % e.i) != 0)
                                        continue;

                                if (!e.r)
                                        continue;

                                e.r = false;

                                Promise.resolve(e.fn()).finally((function() { this.r = true }).bind(e));
                        }

                        Poll.tick = (Poll.tick + 1) % Math.pow(2, 32);
                },

                /**
                 * Test whether the polling loop is running.
                 *
                 * @instance
                 * @memberof LuCI.Poll
                 * @returns {boolean} - Returns `true` if polling is active, else `false`.
                 */
                active: function() {
                        return (this.timer != null);
                }
        });


        var dummyElem = null,
            domParser = null,
            originalCBIInit = null,
            rpcBaseURL = null,
            sysFeatures = null,
            classes = {};

        var LuCI = Class.extend(/** @lends LuCI.prototype */ {
                __name__: 'LuCI',
                __init__: function(env) {

                        document.querySelectorAll('script[src*="/luci.js"]').forEach(function(s) {
                                if (env.base_url == null || env.base_url == '') {
                                        var m = (s.getAttribute('src') || '').match(/^(.*)\/luci\.js(?:\?v=([^?]+))?$/);
                                        if (m) {
                                                env.base_url = m[1];
                                                env.resource_version = m[2];
                                        }
                                }
                        });

                        if (env.base_url == null)
                                this.error('InternalError', 'Cannot find url of luci.js');

                        env.cgi_base = env.scriptname.replace(/\/[^\/]+$/, '');

                        Object.assign(this.env, env);

                        document.addEventListener('poll-start', function(ev) {
                                document.querySelectorAll('[id^="xhr_poll_status"]').forEach(function(e) {
                                        e.style.display = (e.id == 'xhr_poll_status_off') ? 'none' : '';
                                });
                        });

                        document.addEventListener('poll-stop', function(ev) {
                                document.querySelectorAll('[id^="xhr_poll_status"]').forEach(function(e) {
                                        e.style.display = (e.id == 'xhr_poll_status_on') ? 'none' : '';
                                });
                        });

                        var domReady = new Promise(function(resolveFn, rejectFn) {
                                document.addEventListener('DOMContentLoaded', resolveFn);
                        });

                        Promise.all([
                                domReady,
                                this.require('ui'),
                                this.require('rpc'),
                                this.require('form'),
                                this.probeRPCBaseURL()
                        ]).then(this.setupDOM.bind(this)).catch(this.error);

                        originalCBIInit = window.cbi_init;
                        window.cbi_init = function() {};
                },

                /**
                 * Captures the current stack trace and throws an error of the
                 * specified type as a new exception. Also logs the exception as
                 * error to the debug console if it is available.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {Error|string} [type=Error]
                 * Either a string specifying the type of the error to throw or an
                 * existing `Error` instance to copy.
                 *
                 * @param {string} [fmt=Unspecified error]
                 * A format string which is used to form the error message, together
                 * with all subsequent optional arguments.
                 *
                 * @param {...*} [args]
                 * Zero or more variable arguments to the supplied format string.
                 *
                 * @throws {Error}
                 * Throws the created error object with the captured stack trace
                 * appended to the message and the type set to the given type
                 * argument or copied from the given error instance.
                 */
                raise: function(type, fmt /*, ...*/) {
                        var e = null,
                            msg = fmt ? String.prototype.format.apply(fmt, this.varargs(arguments, 2)) : null,
                            stack = null;

                        if (type instanceof Error) {
                                e = type;

                                if (msg)
                                        e.message = msg + ': ' + e.message;
                        }
                        else {
                                try { throw new Error('stacktrace') }
                                catch (e2) { stack = (e2.stack || '').split(/\n/) }

                                e = new (window[type || 'Error'] || Error)(msg || 'Unspecified error');
                                e.name = type || 'Error';
                        }

                        stack = (stack || []).map(function(frame) {
                                frame = frame.replace(/(.*?)@(.+):(\d+):(\d+)/g, 'at $1 ($2:$3:$4)').trim();
                                return frame ? '  ' + frame : '';
                        });

                        if (!/^  at /.test(stack[0]))
                                stack.shift();

                        if (/\braise /.test(stack[0]))
                                stack.shift();

                        if (/\berror /.test(stack[0]))
                                stack.shift();

                        if (stack.length)
                                e.message += '\n' + stack.join('\n');

                        if (window.console && console.debug)
                                console.debug(e);

                        throw e;
                },

                /**
                 * A wrapper around {@link LuCI#raise raise()} which also renders
                 * the error either as modal overlay when `ui.js` is already loaed
                 * or directly into the view body.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {Error|string} [type=Error]
                 * Either a string specifying the type of the error to throw or an
                 * existing `Error` instance to copy.
                 *
                 * @param {string} [fmt=Unspecified error]
                 * A format string which is used to form the error message, together
                 * with all subsequent optional arguments.
                 *
                 * @param {...*} [args]
                 * Zero or more variable arguments to the supplied format string.
                 *
                 * @throws {Error}
                 * Throws the created error object with the captured stack trace
                 * appended to the message and the type set to the given type
                 * argument or copied from the given error instance.
                 */
                error: function(type, fmt /*, ...*/) {
                        try {
                                L.raise.apply(L, Array.prototype.slice.call(arguments));
                        }
                        catch (e) {
                                if (!e.reported) {
                                        if (L.ui)
                                                L.ui.addNotification(e.name || _('Runtime error'),
                                                        E('pre', {}, e.message), 'danger');
                                        else
                                                L.dom.content(document.querySelector('#maincontent'),
                                                        E('pre', { 'class': 'alert-message error' }, e.message));

                                        e.reported = true;
                                }

                                throw e;
                        }
                },

                /**
                 * Return a bound function using the given `self` as `this` context
                 * and any further arguments as parameters to the bound function.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {function} fn
                 * The function to bind.
                 *
                 * @param {*} self
                 * The value to bind as `this` context to the specified function.
                 *
                 * @param {...*} [args]
                 * Zero or more variable arguments which are bound to the function
                 * as parameters.
                 *
                 * @returns {function}
                 * Returns the bound function.
                 */
                bind: function(fn, self /*, ... */) {
                        return Function.prototype.bind.apply(fn, this.varargs(arguments, 2, self));
                },

                /**
                 * Load an additional LuCI JavaScript class and its dependencies,
                 * instantiate it and return the resulting class instance. Each
                 * class is only loaded once. Subsequent attempts to load the same
                 * class will return the already instantiated class.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string} name
                 * The name of the class to load in dotted notation. Dots will
                 * be replaced by spaces and joined with the runtime-determined
                 * base URL of LuCI.js to form an absolute URL to load the class
                 * file from.
                 *
                 * @throws {DependencyError}
                 * Throws a `DependencyError` when the class to load includes
                 * circular dependencies.
                 *
                 * @throws {NetworkError}
                 * Throws `NetworkError` when the underlying {@link LuCI.Request}
                 * call failed.
                 *
                 * @throws {SyntaxError}
                 * Throws `SyntaxError` when the loaded class file code cannot
                 * be interpreted by `eval`.
                 *
                 * @throws {TypeError}
                 * Throws `TypeError` when the class file could be loaded and
                 * interpreted, but when invoking its code did not yield a valid
                 * class instance.
                 *
                 * @returns {Promise<LuCI#Class>}
                 * Returns the instantiated class.
                 */
                require: function(name, from) {
                        var L = this, url = null, from = from || [];

                        /* Class already loaded */
                        if (classes[name] != null) {
                                /* Circular dependency */
                                if (from.indexOf(name) != -1)
                                        L.raise('DependencyError',
                                                'Circular dependency: class "%s" depends on "%s"',
                                                name, from.join('" which depends on "'));

                                return Promise.resolve(classes[name]);
                        }

                        url = '%s/%s.js%s'.format(L.env.base_url, name.replace(/\./g, '/'), (L.env.resource_version ? '?v=' + L.env.resource_version : ''));
                        from = [ name ].concat(from);

                        var compileClass = function(res) {
                                if (!res.ok)
                                        L.raise('NetworkError',
                                                'HTTP error %d while loading class file "%s"', res.status, url);

                                var source = res.text(),
                                    requirematch = /^require[ \t]+(\S+)(?:[ \t]+as[ \t]+([a-zA-Z_]\S*))?$/,
                                    strictmatch = /^use[ \t]+strict$/,
                                    depends = [],
                                    args = '';

                                /* find require statements in source */
                                for (var i = 0, off = -1, quote = -1, esc = false; i < source.length; i++) {
                                        var chr = source.charCodeAt(i);

                                        if (esc) {
                                                esc = false;
                                        }
                                        else if (chr == 92) {
                                                esc = true;
                                        }
                                        else if (chr == quote) {
                                                var s = source.substring(off, i),
                                                    m = requirematch.exec(s);

                                                if (m) {
                                                        var dep = m[1], as = m[2] || dep.replace(/[^a-zA-Z0-9_]/g, '_');
                                                        depends.push(L.require(dep, from));
                                                        args += ', ' + as;
                                                }
                                                else if (!strictmatch.exec(s)) {
                                                        break;
                                                }

                                                off = -1;
                                                quote = -1;
                                        }
                                        else if (quote == -1 && (chr == 34 || chr == 39)) {
                                                off = i + 1;
                                                quote = chr;
                                        }
                                }

                                /* load dependencies and instantiate class */
                                return Promise.all(depends).then(function(instances) {
                                        var _factory, _class;

                                        try {
                                                _factory = eval(
                                                        '(function(window, document, L%s) { %s })\n\n//# sourceURL=%s\n'
                                                                .format(args, source, res.url));
                                        }
                                        catch (error) {
                                                L.raise('SyntaxError', '%s\n  in %s:%s',
                                                        error.message, res.url, error.lineNumber || '?');
                                        }

                                        _factory.displayName = toCamelCase(name + 'ClassFactory');
                                        _class = _factory.apply(_factory, [window, document, L].concat(instances));

                                        if (!Class.isSubclass(_class))
                                            L.error('TypeError', '"%s" factory yields invalid constructor', name);

                                        if (_class.displayName == 'AnonymousClass')
                                                _class.displayName = toCamelCase(name + 'Class');

                                        var ptr = Object.getPrototypeOf(L),
                                            parts = name.split(/\./),
                                            instance = new _class();

                                        for (var i = 0; ptr && i < parts.length - 1; i++)
                                                ptr = ptr[parts[i]];

                                        if (ptr)
                                                ptr[parts[i]] = instance;

                                        classes[name] = instance;

                                        return instance;
                                });
                        };

                        /* Request class file */
                        classes[name] = Request.get(url, { cache: true }).then(compileClass);

                        return classes[name];
                },

                /* DOM setup */
                probeRPCBaseURL: function() {
                        if (rpcBaseURL == null) {
                                try {
                                        rpcBaseURL = window.sessionStorage.getItem('rpcBaseURL');
                                }
                                catch (e) { }
                        }

                        if (rpcBaseURL == null) {
                                var rpcFallbackURL = this.url('admin/ubus');

                                rpcBaseURL = Request.get(this.env.ubuspath).then(function(res) {
                                        return (rpcBaseURL = (res.status == 400) ? L.env.ubuspath : rpcFallbackURL);
                                }, function() {
                                        return (rpcBaseURL = rpcFallbackURL);
                                }).then(function(url) {
                                        try {
                                                window.sessionStorage.setItem('rpcBaseURL', url);
                                        }
                                        catch (e) { }

                                        return url;
                                });
                        }

                        return Promise.resolve(rpcBaseURL);
                },

                probeSystemFeatures: function() {
                        var sessionid = classes.rpc.getSessionID();

                        if (sysFeatures == null) {
                                try {
                                        var data = JSON.parse(window.sessionStorage.getItem('sysFeatures'));

                                        if (this.isObject(data) && this.isObject(data[sessionid]))
                                                sysFeatures = data[sessionid];
                                }
                                catch (e) {}
                        }

                        if (!this.isObject(sysFeatures)) {
                                sysFeatures = classes.rpc.declare({
                                        object: 'luci',
                                        method: 'getFeatures',
                                        expect: { '': {} }
                                })().then(function(features) {
                                        try {
                                                var data = {};
                                                    data[sessionid] = features;

                                                window.sessionStorage.setItem('sysFeatures', JSON.stringify(data));
                                        }
                                        catch (e) {}

                                        sysFeatures = features;

                                        return features;
                                });
                        }

                        return Promise.resolve(sysFeatures);
                },

                /**
                 * Test whether a particular system feature is available, such as
                 * hostapd SAE support or an installed firewall. The features are
                 * queried once at the beginning of the LuCI session and cached in
                 * `SessionStorage` throughout the lifetime of the associated tab or
                 * browser window.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string} feature
                 * The feature to test. For detailed list of known feature flags,
                 * see `/modules/luci-base/root/usr/libexec/rpcd/luci`.
                 *
                 * @param {string} [subfeature]
                 * Some feature classes like `hostapd` provide sub-feature flags,
                 * such as `sae` or `11w` support. The `subfeature` argument can
                 * be used to query these.
                 *
                 * @return {boolean|null}
                 * Return `true` if the queried feature (and sub-feature) is available
                 * or `false` if the requested feature isn't present or known.
                 * Return `null` when a sub-feature was queried for a feature which
                 * has no sub-features.
                 */
                hasSystemFeature: function() {
                        var ft = sysFeatures[arguments[0]];

                        if (arguments.length == 2)
                                return this.isObject(ft) ? ft[arguments[1]] : null;

                        return (ft != null && ft != false);
                },

                /* private */
                notifySessionExpiry: function() {
                        Poll.stop();

                        L.ui.showModal(_('Session expired'), [
                                E('div', { class: 'alert-message warning' },
                                        _('A new login is required since the authentication session expired.')),
                                E('div', { class: 'right' },
                                        E('div', {
                                                class: 'btn primary',
                                                click: function() {
                                                        var loc = window.location;
                                                        window.location = loc.protocol + '//' + loc.host + loc.pathname + loc.search;
                                                }
                                        }, _('To login…')))
                        ]);

                        L.raise('SessionError', 'Login session is expired');
                },

                /* private */
                setupDOM: function(res) {
                        var domEv = res[0],
                            uiClass = res[1],
                            rpcClass = res[2],
                            formClass = res[3],
                            rpcBaseURL = res[4];

                        rpcClass.setBaseURL(rpcBaseURL);

                        rpcClass.addInterceptor(function(msg, req) {
                                if (!L.isObject(msg) || !L.isObject(msg.error) || msg.error.code != -32002)
                                        return;

                                if (!L.isObject(req) || (req.object == 'session' && req.method == 'access'))
                                        return;

                                return rpcClass.declare({
                                        'object': 'session',
                                        'method': 'access',
                                        'params': [ 'scope', 'object', 'function' ],
                                        'expect': { access: true }
                                })('uci', 'luci', 'read').catch(L.notifySessionExpiry);
                        });

                        Request.addInterceptor(function(res) {
                                var isDenied = false;

                                if (res.status == 403 && res.headers.get('X-LuCI-Login-Required') == 'yes')
                                        isDenied = true;

                                if (!isDenied)
                                        return;

                                L.notifySessionExpiry();
                        });

                        return this.probeSystemFeatures().finally(this.initDOM);
                },

                /* private */
                initDOM: function() {
                        originalCBIInit();
                        Poll.start();
                        document.dispatchEvent(new CustomEvent('luci-loaded'));
                },

                /**
                 * The `env` object holds environment settings used by LuCI, such
                 * as request timeouts, base URLs etc.
                 *
                 * @instance
                 * @memberof LuCI
                 */
                env: {},

                /**
                 * Construct a relative URL path from the given prefix and parts.
                 * The resulting URL is guaranteed to only contain the characters
                 * `a-z`, `A-Z`, `0-9`, `_`, `.`, `%`, `,`, `;`, and `-` as well
                 * as `/` for the path separator.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string} [prefix]
                 * The prefix to join the given parts with. If the `prefix` is
                 * omitted, it defaults to an empty string.
                 *
                 * @param {string[]} [parts]
                 * An array of parts to join into an URL path. Parts may contain
                 * slashes and any of the other characters mentioned above.
                 *
                 * @return {string}
                 * Return the joined URL path.
                 */
                path: function(prefix, parts) {
                        var url = [ prefix || '' ];

                        for (var i = 0; i < parts.length; i++)
                                if (/^(?:[a-zA-Z0-9_.%,;-]+\/)*[a-zA-Z0-9_.%,;-]+$/.test(parts[i]))
                                        url.push('/', parts[i]);

                        if (url.length === 1)
                                url.push('/');

                        return url.join('');
                },

                /**
                 * Construct an URL  pathrelative to the script path of the server
                 * side LuCI application (usually `/cgi-bin/luci`).
                 *
                 * The resulting URL is guaranteed to only contain the characters
                 * `a-z`, `A-Z`, `0-9`, `_`, `.`, `%`, `,`, `;`, and `-` as well
                 * as `/` for the path separator.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string[]} [parts]
                 * An array of parts to join into an URL path. Parts may contain
                 * slashes and any of the other characters mentioned above.
                 *
                 * @return {string}
                 * Returns the resulting URL path.
                 */
                url: function() {
                        return this.path(this.env.scriptname, arguments);
                },

                /**
                 * Construct an URL path relative to the global static resource path
                 * of the LuCI ui (usually `/luci-static/resources`).
                 *
                 * The resulting URL is guaranteed to only contain the characters
                 * `a-z`, `A-Z`, `0-9`, `_`, `.`, `%`, `,`, `;`, and `-` as well
                 * as `/` for the path separator.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string[]} [parts]
                 * An array of parts to join into an URL path. Parts may contain
                 * slashes and any of the other characters mentioned above.
                 *
                 * @return {string}
                 * Returns the resulting URL path.
                 */
                resource: function() {
                        return this.path(this.env.resource, arguments);
                },

                /**
                 * Construct an URL path relative to the media resource path of the
                 * LuCI ui (usually `/luci-static/$theme_name`).
                 *
                 * The resulting URL is guaranteed to only contain the characters
                 * `a-z`, `A-Z`, `0-9`, `_`, `.`, `%`, `,`, `;`, and `-` as well
                 * as `/` for the path separator.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string[]} [parts]
                 * An array of parts to join into an URL path. Parts may contain
                 * slashes and any of the other characters mentioned above.
                 *
                 * @return {string}
                 * Returns the resulting URL path.
                 */
                media: function() {
                        return this.path(this.env.media, arguments);
                },

                /**
                 * Return the complete URL path to the current view.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @return {string}
                 * Returns the URL path to the current view.
                 */
                location: function() {
                        return this.path(this.env.scriptname, this.env.requestpath);
                },


                /**
                 * Tests whether the passed argument is a JavaScript object.
                 * This function is meant to be an object counterpart to the
                 * standard `Array.isArray()` function.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {*} [val]
                 * The value to test
                 *
                 * @return {boolean}
                 * Returns `true` if the given value is of type object and
                 * not `null`, else returns `false`.
                 */
                isObject: function(val) {
                        return (val != null && typeof(val) == 'object');
                },

                /**
                 * Return an array of sorted object keys, optionally sorted by
                 * a different key or a different sorting mode.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {object} obj
                 * The object to extract the keys from. If the given value is
                 * not an object, the function will return an empty array.
                 *
                 * @param {string} [key]
                 * Specifies the key to order by. This is mainly useful for
                 * nested objects of objects or objects of arrays when sorting
                 * shall not be performed by the primary object keys but by
                 * some other key pointing to a value within the nested values.
                 *
                 * @param {string} [sortmode]
                 * May be either `addr` or `num` to override the natural
                 * lexicographic sorting with a sorting suitable for IP/MAC style
                 * addresses or numeric values respectively.
                 *
                 * @return {string[]}
                 * Returns an array containing the sorted keys of the given object.
                 */
                sortedKeys: function(obj, key, sortmode) {
                        if (obj == null || typeof(obj) != 'object')
                                return [];

                        return Object.keys(obj).map(function(e) {
                                var v = (key != null) ? obj[e][key] : e;

                                switch (sortmode) {
                                case 'addr':
                                        v = (v != null) ? v.replace(/(?:^|[.:])([0-9a-fA-F]{1,4})/g,
                                                function(m0, m1) { return ('000' + m1.toLowerCase()).substr(-4) }) : null;
                                        break;

                                case 'num':
                                        v = (v != null) ? +v : null;
                                        break;
                                }

                                return [ e, v ];
                        }).filter(function(e) {
                                return (e[1] != null);
                        }).sort(function(a, b) {
                                return (a[1] > b[1]);
                        }).map(function(e) {
                                return e[0];
                        });
                },

                /**
                 * Converts the given value to an array. If the given value is of
                 * type array, it is returned as-is, values of type object are
                 * returned as one-element array containing the object, empty
                 * strings and `null` values are returned as empty array, all other
                 * values are converted using `String()`, trimmed, split on white
                 * space and returned as array.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {*} val
                 * The value to convert into an array.
                 *
                 * @return {Array<*>}
                 * Returns the resulting array.
                 */
                toArray: function(val) {
                        if (val == null)
                                return [];
                        else if (Array.isArray(val))
                                return val;
                        else if (typeof(val) == 'object')
                                return [ val ];

                        var s = String(val).trim();

                        if (s == '')
                                return [];

                        return s.split(/\s+/);
                },

                /**
                 * Returns a promise resolving with either the given value or or with
                 * the given default in case the input value is a rejecting promise.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {*} value
                 * The value to resolve the promise with.
                 *
                 * @param {*} defvalue
                 * The default value to resolve the promise with in case the given
                 * input value is a rejecting promise.
                 *
                 * @returns {Promise<*>}
                 * Returns a new promise resolving either to the given input value or
                 * to the given default value on error.
                 */
                resolveDefault: function(value, defvalue) {
                        return Promise.resolve(value).catch(function() { return defvalue });
                },

                /**
                 * The request callback function is invoked whenever an HTTP
                 * reply to a request made using the `L.get()`, `L.post()` or
                 * `L.poll()` function is timed out or received successfully.
                 *
                 * @instance
                 * @memberof LuCI
                 *
                 * @callback LuCI.requestCallbackFn
                 * @param {XMLHTTPRequest} xhr
                 * The XMLHTTPRequest instance used to make the request.
                 *
                 * @param {*} data
                 * The response JSON if the response could be parsed as such,
                 * else `null`.
                 *
                 * @param {number} duration
                 * The total duration of the request in milliseconds.
                 */

                /**
                 * Issues a GET request to the given url and invokes the specified
                 * callback function. The function is a wrapper around
                 * {@link LuCI.Request#request Request.request()}.
                 *
                 * @deprecated
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string} url
                 * The URL to request.
                 *
                 * @param {Object<string, string>} [args]
                 * Additional query string arguments to append to the URL.
                 *
                 * @param {LuCI.requestCallbackFn} cb
                 * The callback function to invoke when the request finishes.
                 *
                 * @return {Promise<null>}
                 * Returns a promise resolving to `null` when concluded.
                 */
                get: function(url, args, cb) {
                        return this.poll(null, url, args, cb, false);
                },

                /**
                 * Issues a POST request to the given url and invokes the specified
                 * callback function. The function is a wrapper around
                 * {@link LuCI.Request#request Request.request()}. The request is
                 * sent using `application/x-www-form-urlencoded` encoding and will
                 * contain a field `token` with the current value of `LuCI.env.token`
                 * by default.
                 *
                 * @deprecated
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {string} url
                 * The URL to request.
                 *
                 * @param {Object<string, string>} [args]
                 * Additional post arguments to append to the request body.
                 *
                 * @param {LuCI.requestCallbackFn} cb
                 * The callback function to invoke when the request finishes.
                 *
                 * @return {Promise<null>}
                 * Returns a promise resolving to `null` when concluded.
                 */
                post: function(url, args, cb) {
                        return this.poll(null, url, args, cb, true);
                },

                /**
                 * Register a polling HTTP request that invokes the specified
                 * callback function. The function is a wrapper around
                 * {@link LuCI.Request.poll#add Request.poll.add()}.
                 *
                 * @deprecated
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {number} interval
                 * The poll interval to use. If set to a value less than or equal
                 * to `0`, it will default to the global poll interval configured
                 * in `LuCI.env.pollinterval`.
                 *
                 * @param {string} url
                 * The URL to request.
                 *
                 * @param {Object<string, string>} [args]
                 * Specifies additional arguments for the request. For GET requests,
                 * the arguments are appended to the URL as query string, for POST
                 * requests, they'll be added to the request body.
                 *
                 * @param {LuCI.requestCallbackFn} cb
                 * The callback function to invoke whenever a request finishes.
                 *
                 * @param {boolean} [post=false]
                 * When set to `false` or not specified, poll requests will be made
                 * using the GET method. When set to `true`, POST requests will be
                 * issued. In case of POST requests, the request body will contain
                 * an argument `token` with the current value of `LuCI.env.token` by
                 * default, regardless of the parameters specified with `args`.
                 *
                 * @return {function}
                 * Returns the internally created function that has been passed to
                 * {@link LuCI.Request.poll#add Request.poll.add()}. This value can
                 * be passed to {@link LuCI.Poll.remove Poll.remove()} to remove the
                 * polling request.
                 */
                poll: function(interval, url, args, cb, post) {
                        if (interval !== null && interval <= 0)
                                interval = this.env.pollinterval;

                        var data = post ? { token: this.env.token } : null,
                            method = post ? 'POST' : 'GET';

                        if (!/^(?:\/|\S+:\/\/)/.test(url))
                                url = this.url(url);

                        if (args != null)
                                data = Object.assign(data || {}, args);

                        if (interval !== null)
                                return Request.poll.add(interval, url, { method: method, query: data }, cb);
                        else
                                return Request.request(url, { method: method, query: data })
                                        .then(function(res) {
                                                var json = null;
                                                if (/^application\/json\b/.test(res.headers.get('Content-Type')))
                                                        try { json = res.json() } catch(e) {}
                                                cb(res.xhr, json, res.duration);
                                        });
                },

                /**
                 * Deprecated wrapper around {@link LuCI.Poll.remove Poll.remove()}.
                 *
                 * @deprecated
                 * @instance
                 * @memberof LuCI
                 *
                 * @param {function} entry
                 * The polling function to remove.
                 *
                 * @return {boolean}
                 * Returns `true` when the function has been removed or `false` if
                 * it could not be found.
                 */
                stop: function(entry) { return Poll.remove(entry) },

                /**
                 * Deprecated wrapper around {@link LuCI.Poll.stop Poll.stop()}.
                 *
                 * @deprecated
                 * @instance
                 * @memberof LuCI
                 *
                 * @return {boolean}
                 * Returns `true` when the polling loop has been stopped or `false`
                 * when it didn't run to begin with.
                 */
                halt: function() { return Poll.stop() },

                /**
                 * Deprecated wrapper around {@link LuCI.Poll.start Poll.start()}.
                 *
                 * @deprecated
                 * @instance
                 * @memberof LuCI
                 *
                 * @return {boolean}
                 * Returns `true` when the polling loop has been started or `false`
                 * when it was already running.
                 */
                run: function() { return Poll.start() },


                /**
                 * @class
                 * @memberof LuCI
                 * @hideconstructor
                 * @classdesc
                 *
                 * The `dom` class provides convenience method for creating and
                 * manipulating DOM elements.
                 */
                dom: Class.singleton(/* @lends LuCI.dom.prototype */ {
                        __name__: 'LuCI.DOM',

                        /**
                         * Tests whether the given argument is a valid DOM `Node`.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {*} e
                         * The value to test.
                         *
                         * @returns {boolean}
                         * Returns `true` if the value is a DOM `Node`, else `false`.
                         */
                        elem: function(e) {
                                return (e != null && typeof(e) == 'object' && 'nodeType' in e);
                        },

                        /**
                         * Parses a given string as HTML and returns the first child node.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {string} s
                         * A string containing an HTML fragment to parse. Note that only
                         * the first result of the resulting structure is returned, so an
                         * input value of `<div>foo</div> <div>bar</div>` will only return
                         * the first `div` element node.
                         *
                         * @returns {Node}
                         * Returns the first DOM `Node` extracted from the HTML fragment or
                         * `null` on parsing failures or if no element could be found.
                         */
                        parse: function(s) {
                                var elem;

                                try {
                                        domParser = domParser || new DOMParser();
                                        elem = domParser.parseFromString(s, 'text/html').body.firstChild;
                                }
                                catch(e) {}

                                if (!elem) {
                                        try {
                                                dummyElem = dummyElem || document.createElement('div');
                                                dummyElem.innerHTML = s;
                                                elem = dummyElem.firstChild;
                                        }
                                        catch (e) {}
                                }

                                return elem || null;
                        },

                        /**
                         * Tests whether a given `Node` matches the given query selector.
                         *
                         * This function is a convenience wrapper around the standard
                         * `Node.matches("selector")` function with the added benefit that
                         * the `node` argument may be a non-`Node` value, in which case
                         * this function simply returns `false`.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {*} node
                         * The `Node` argument to test the selector against.
                         *
                         * @param {string} [selector]
                         * The query selector expression to test against the given node.
                         *
                         * @returns {boolean}
                         * Returns `true` if the given node matches the specified selector
                         * or `false` when the node argument is no valid DOM `Node` or the
                         * selector didn't match.
                         */
                        matches: function(node, selector) {
                                var m = this.elem(node) ? node.matches || node.msMatchesSelector : null;
                                return m ? m.call(node, selector) : false;
                        },

                        /**
                         * Returns the closest parent node that matches the given query
                         * selector expression.
                         *
                         * This function is a convenience wrapper around the standard
                         * `Node.closest("selector")` function with the added benefit that
                         * the `node` argument may be a non-`Node` value, in which case
                         * this function simply returns `null`.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {*} node
                         * The `Node` argument to find the closest parent for.
                         *
                         * @param {string} [selector]
                         * The query selector expression to test against each parent.
                         *
                         * @returns {Node|null}
                         * Returns the closest parent node matching the selector or
                         * `null` when the node argument is no valid DOM `Node` or the
                         * selector didn't match any parent.
                         */
                        parent: function(node, selector) {
                                if (this.elem(node) && node.closest)
                                        return node.closest(selector);

                                while (this.elem(node))
                                        if (this.matches(node, selector))
                                                return node;
                                        else
                                                node = node.parentNode;

                                return null;
                        },

                        /**
                         * Appends the given children data to the given node.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {*} node
                         * The `Node` argument to append the children to.
                         *
                         * @param {*} [children]
                         * The childrens to append to the given node.
                         *
                         * When `children` is an array, then each item of the array
                         * will be either appended as child element or text node,
                         * depending on whether the item is a DOM `Node` instance or
                         * some other non-`null` value. Non-`Node`, non-`null` values
                         * will be converted to strings first before being passed as
                         * argument to `createTextNode()`.
                         *
                         * When `children` is a function, it will be invoked with
                         * the passed `node` argument as sole parameter and the `append`
                         * function will be invoked again, with the given `node` argument
                         * as first and the return value of the `children` function as
                         * second parameter.
                         *
                         * When `children` is is a DOM `Node` instance, it will be
                         * appended to the given `node`.
                         *
                         * When `children` is any other non-`null` value, it will be
                         * converted to a string and appened to the `innerHTML` property
                         * of the given `node`.
                         *
                         * @returns {Node|null}
                         * Returns the last children `Node` appended to the node or `null`
                         * if either the `node` argument was no valid DOM `node` or if the
                         * `children` was `null` or didn't result in further DOM nodes.
                         */
                        append: function(node, children) {
                                if (!this.elem(node))
                                        return null;

                                if (Array.isArray(children)) {
                                        for (var i = 0; i < children.length; i++)
                                                if (this.elem(children[i]))
                                                        node.appendChild(children[i]);
                                                else if (children !== null && children !== undefined)
                                                        node.appendChild(document.createTextNode('' + children[i]));

                                        return node.lastChild;
                                }
                                else if (typeof(children) === 'function') {
                                        return this.append(node, children(node));
                                }
                                else if (this.elem(children)) {
                                        return node.appendChild(children);
                                }
                                else if (children !== null && children !== undefined) {
                                        node.innerHTML = '' + children;
                                        return node.lastChild;
                                }

                                return null;
                        },

                        /**
                         * Replaces the content of the given node with the given children.
                         *
                         * This function first removes any children of the given DOM
                         * `Node` and then adds the given given children following the
                         * rules outlined below.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {*} node
                         * The `Node` argument to replace the children of.
                         *
                         * @param {*} [children]
                         * The childrens to replace into the given node.
                         *
                         * When `children` is an array, then each item of the array
                         * will be either appended as child element or text node,
                         * depending on whether the item is a DOM `Node` instance or
                         * some other non-`null` value. Non-`Node`, non-`null` values
                         * will be converted to strings first before being passed as
                         * argument to `createTextNode()`.
                         *
                         * When `children` is a function, it will be invoked with
                         * the passed `node` argument as sole parameter and the `append`
                         * function will be invoked again, with the given `node` argument
                         * as first and the return value of the `children` function as
                         * second parameter.
                         *
                         * When `children` is is a DOM `Node` instance, it will be
                         * appended to the given `node`.
                         *
                         * When `children` is any other non-`null` value, it will be
                         * converted to a string and appened to the `innerHTML` property
                         * of the given `node`.
                         *
                         * @returns {Node|null}
                         * Returns the last children `Node` appended to the node or `null`
                         * if either the `node` argument was no valid DOM `node` or if the
                         * `children` was `null` or didn't result in further DOM nodes.
                         */
                        content: function(node, children) {
                                if (!this.elem(node))
                                        return null;

                                var dataNodes = node.querySelectorAll('[data-idref]');

                                for (var i = 0; i < dataNodes.length; i++)
                                        delete this.registry[dataNodes[i].getAttribute('data-idref')];

                                while (node.firstChild)
                                        node.removeChild(node.firstChild);

                                return this.append(node, children);
                        },

                        /**
                         * Sets attributes or registers event listeners on element nodes.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {*} node
                         * The `Node` argument to set the attributes or add the event
                         * listeners for. When the given `node` value is not a valid
                         * DOM `Node`, the function returns and does nothing.
                         *
                         * @param {string|Object<string, *>} key
                         * Specifies either the attribute or event handler name to use,
                         * or an object containing multiple key, value pairs which are
                         * each added to the node as either attribute or event handler,
                         * depending on the respective value.
                         *
                         * @param {*} [val]
                         * Specifies the attribute value or event handler function to add.
                         * If the `key` parameter is an `Object`, this parameter will be
                         * ignored.
                         *
                         * When `val` is of type function, it will be registered as event
                         * handler on the given `node` with the `key` parameter being the
                         * event name.
                         *
                         * When `val` is of type object, it will be serialized as JSON and
                         * added as attribute to the given `node`, using the given `key`
                         * as attribute name.
                         *
                         * When `val` is of any other type, it will be added as attribute
                         * to the given `node` as-is, with the underlying `setAttribute()`
                         * call implicitely turning it into a string.
                         */
                        attr: function(node, key, val) {
                                if (!this.elem(node))
                                        return null;

                                var attr = null;

                                if (typeof(key) === 'object' && key !== null)
                                        attr = key;
                                else if (typeof(key) === 'string')
                                        attr = {}, attr[key] = val;

                                for (key in attr) {
                                        if (!attr.hasOwnProperty(key) || attr[key] == null)
                                                continue;

                                        switch (typeof(attr[key])) {
                                        case 'function':
                                                node.addEventListener(key, attr[key]);
                                                break;

                                        case 'object':
                                                node.setAttribute(key, JSON.stringify(attr[key]));
                                                break;

                                        default:
                                                node.setAttribute(key, attr[key]);
                                        }
                                }
                        },

                        /**
                         * Creates a new DOM `Node` from the given `html`, `attr` and
                         * `data` parameters.
                         *
                         * This function has multiple signatures, it can be either invoked
                         * in the form `create(html[, attr[, data]])` or in the form
                         * `create(html[, data])`. The used variant is determined from the
                         * type of the second argument.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {*} html
                         * Describes the node to create.
                         *
                         * When the value of `html` is of type array, a `DocumentFragment`
                         * node is created and each item of the array is first converted
                         * to a DOM `Node` by passing it through `create()` and then added
                         * as child to the fragment.
                         *
                         * When the value of `html` is a DOM `Node` instance, no new
                         * element will be created but the node will be used as-is.
                         *
                         * When the value of `html` is a string starting with `<`, it will
                         * be passed to `dom.parse()` and the resulting value is used.
                         *
                         * When the value of `html` is any other string, it will be passed
                         * to `document.createElement()` for creating a new DOM `Node` of
                         * the given name.
                         *
                         * @param {Object<string, *>} [attr]
                         * Specifies an Object of key, value pairs to set as attributes
                         * or event handlers on the created node. Refer to
                         * {@link LuCI.dom#attr dom.attr()} for details.
                         *
                         * @param {*} [data]
                         * Specifies children to append to the newly created element.
                         * Refer to {@link LuCI.dom#append dom.append()} for details.
                         *
                         * @throws {InvalidCharacterError}
                         * Throws an `InvalidCharacterError` when the given `html`
                         * argument contained malformed markup (such as not escaped
                         * `&` characters in XHTML mode) or when the given node name
                         * in `html` contains characters which are not legal in DOM
                         * element names, such as spaces.
                         *
                         * @returns {Node}
                         * Returns the newly created `Node`.
                         */
                        create: function() {
                                var html = arguments[0],
                                    attr = arguments[1],
                                    data = arguments[2],
                                    elem;

                                if (!(attr instanceof Object) || Array.isArray(attr))
                                        data = attr, attr = null;

                                if (Array.isArray(html)) {
                                        elem = document.createDocumentFragment();
                                        for (var i = 0; i < html.length; i++)
                                                elem.appendChild(this.create(html[i]));
                                }
                                else if (this.elem(html)) {
                                        elem = html;
                                }
                                else if (html.charCodeAt(0) === 60) {
                                        elem = this.parse(html);
                                }
                                else {
                                        elem = document.createElement(html);
                                }

                                if (!elem)
                                        return null;

                                this.attr(elem, attr);
                                this.append(elem, data);

                                return elem;
                        },

                        registry: {},

                        /**
                         * Attaches or detaches arbitrary data to and from a DOM `Node`.
                         *
                         * This function is useful to attach non-string values or runtime
                         * data that is not serializable to DOM nodes. To decouple data
                         * from the DOM, values are not added directly to nodes, but
                         * inserted into a registry instead which is then referenced by a
                         * string key stored as `data-idref` attribute in the node.
                         *
                         * This function has multiple signatures and is sensitive to the
                         * number of arguments passed to it.
                         *
                         *  - `dom.data(node)` -
                         *     Fetches all data associated with the given node.
                         *  - `dom.data(node, key)` -
                         *     Fetches a specific key associated with the given node.
                         *  - `dom.data(node, key, val)` -
                         *     Sets a specific key to the given value associated with the
                         *     given node.
                         *  - `dom.data(node, null)` -
                         *     Clears any data associated with the node.
                         *  - `dom.data(node, key, null)` -
                         *     Clears the given key associated with the node.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {Node} node
                         * The DOM `Node` instance to set or retrieve the data for.
                         *
                         * @param {string|null} [key]
                         * This is either a string specifying the key to retrieve, or
                         * `null` to unset the entire node data.
                         *
                         * @param {*|null} [val]
                         * This is either a non-`null` value to set for a given key or
                         * `null` to remove the given `key` from the specified node.
                         *
                         * @returns {*}
                         * Returns the get or set value, or `null` when no value could
                         * be found.
                         */
                        data: function(node, key, val) {
                                var id = node.getAttribute('data-idref');

                                /* clear all data */
                                if (arguments.length > 1 && key == null) {
                                        if (id != null) {
                                                node.removeAttribute('data-idref');
                                                val = this.registry[id]
                                                delete this.registry[id];
                                                return val;
                                        }

                                        return null;
                                }

                                /* clear a key */
                                else if (arguments.length > 2 && key != null && val == null) {
                                        if (id != null) {
                                                val = this.registry[id][key];
                                                delete this.registry[id][key];
                                                return val;
                                        }

                                        return null;
                                }

                                /* set a key */
                                else if (arguments.length > 2 && key != null && val != null) {
                                        if (id == null) {
                                                do { id = Math.floor(Math.random() * 0xffffffff).toString(16) }
                                                while (this.registry.hasOwnProperty(id));

                                                node.setAttribute('data-idref', id);
                                                this.registry[id] = {};
                                        }

                                        return (this.registry[id][key] = val);
                                }

                                /* get all data */
                                else if (arguments.length == 1) {
                                        if (id != null)
                                                return this.registry[id];

                                        return null;
                                }

                                /* get a key */
                                else if (arguments.length == 2) {
                                        if (id != null)
                                                return this.registry[id][key];
                                }

                                return null;
                        },

                        /**
                         * Binds the given class instance ot the specified DOM `Node`.
                         *
                         * This function uses the `dom.data()` facility to attach the
                         * passed instance of a Class to a node. This is needed for
                         * complex widget elements or similar where the corresponding
                         * class instance responsible for the element must be retrieved
                         * from DOM nodes obtained by `querySelector()` or similar means.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {Node} node
                         * The DOM `Node` instance to bind the class to.
                         *
                         * @param {Class} inst
                         * The Class instance to bind to the node.
                         *
                         * @throws {TypeError}
                         * Throws a `TypeError` when the given instance argument isn't
                         * a valid Class instance.
                         *
                         * @returns {Class}
                         * Returns the bound class instance.
                         */
                        bindClassInstance: function(node, inst) {
                                if (!(inst instanceof Class))
                                        L.error('TypeError', 'Argument must be a class instance');

                                return this.data(node, '_class', inst);
                        },

                        /**
                         * Finds a bound class instance on the given node itself or the
                         * first bound instance on its closest parent node.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {Node} node
                         * The DOM `Node` instance to start from.
                         *
                         * @returns {Class|null}
                         * Returns the founds class instance if any or `null` if no bound
                         * class could be found on the node itself or any of its parents.
                         */
                        findClassInstance: function(node) {
                                var inst = null;

                                do {
                                        inst = this.data(node, '_class');
                                        node = node.parentNode;
                                }
                                while (!(inst instanceof Class) && node != null);

                                return inst;
                        },

                        /**
                         * Finds a bound class instance on the given node itself or the
                         * first bound instance on its closest parent node and invokes
                         * the specified method name on the found class instance.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {Node} node
                         * The DOM `Node` instance to start from.
                         *
                         * @param {string} method
                         * The name of the method to invoke on the found class instance.
                         *
                         * @param {...*} params
                         * Additional arguments to pass to the invoked method as-is.
                         *
                         * @returns {*|null}
                         * Returns the return value of the invoked method if a class
                         * instance and method has been found. Returns `null` if either
                         * no bound class instance could be found, or if the found
                         * instance didn't have the requested `method`.
                         */
                        callClassMethod: function(node, method /*, ... */) {
                                var inst = this.findClassInstance(node);

                                if (inst == null || typeof(inst[method]) != 'function')
                                        return null;

                                return inst[method].apply(inst, inst.varargs(arguments, 2));
                        },

                        /**
                         * The ignore callback function is invoked by `isEmpty()` for each
                         * child node to decide whether to ignore a child node or not.
                         *
                         * When this function returns `false`, the node passed to it is
                         * ignored, else not.
                         *
                         * @callback LuCI.dom~ignoreCallbackFn
                         * @param {Node} node
                         * The child node to test.
                         *
                         * @returns {boolean}
                         * Boolean indicating whether to ignore the node or not.
                         */

                        /**
                         * Tests whether a given DOM `Node` instance is empty or appears
                         * empty.
                         *
                         * Any element child nodes which have the CSS class `hidden` set
                         * or for which the optionally passed `ignoreFn` callback function
                         * returns `false` are ignored.
                         *
                         * @instance
                         * @memberof LuCI.dom
                         * @param {Node} node
                         * The DOM `Node` instance to test.
                         *
                         * @param {LuCI.dom~ignoreCallbackFn} [ignoreFn]
                         * Specifies an optional function which is invoked for each child
                         * node to decide whether the child node should be ignored or not.
                         *
                         * @returns {boolean}
                         * Returns `true` if the node does not have any children or if
                         * any children node either has a `hidden` CSS class or a `false`
                         * result when testing it using the given `ignoreFn`.
                         */
                        isEmpty: function(node, ignoreFn) {
                                for (var child = node.firstElementChild; child != null; child = child.nextElementSibling)
                                        if (!child.classList.contains('hidden') && (!ignoreFn || !ignoreFn(child)))
                                                return false;

                                return true;
                        }
                }),

                Poll: Poll,
                Class: Class,
                Request: Request,

                /**
                 * @class
                 * @memberof LuCI
                 * @hideconstructor
                 * @classdesc
                 *
                 * The `view` class forms the basis of views and provides a standard
                 * set of methods to inherit from.
                 */
                view: Class.extend(/* @lends LuCI.view.prototype */ {
                        __name__: 'LuCI.View',

                        __init__: function() {
                                var vp = document.getElementById('view');

                                L.dom.content(vp, E('div', { 'class': 'spinning' }, _('Loading view…')));

                                return Promise.resolve(this.load())
                                        .then(L.bind(this.render, this))
                                        .then(L.bind(function(nodes) {
                                                var vp = document.getElementById('view');

                                                L.dom.content(vp, nodes);
                                                L.dom.append(vp, this.addFooter());
                                        }, this)).catch(L.error);
                        },

                        /**
                         * The load function is invoked before the view is rendered.
                         *
                         * The invocation of this function is wrapped by
                         * `Promise.resolve()` so it may return Promises if needed.
                         *
                         * The return value of the function (or the resolved values
                         * of the promise returned by it) will be passed as first
                         * argument to `render()`.
                         *
                         * This function is supposed to be overwritten by subclasses,
                         * the default implementation does nothing.
                         *
                         * @instance
                         * @abstract
                         * @memberof LuCI.view
                         *
                         * @returns {*|Promise<*>}
                         * May return any value or a Promise resolving to any value.
                         */
                        load: function() {},

                        /**
                         * The render function is invoked after the
                         * {@link LuCI.view#load load()} function and responsible
                         * for setting up the view contents. It must return a DOM
                         * `Node` or `DocumentFragment` holding the contents to
                         * insert into the view area.
                         *
                         * The invocation of this function is wrapped by
                         * `Promise.resolve()` so it may return Promises if needed.
                         *
                         * The return value of the function (or the resolved values
                         * of the promise returned by it) will be inserted into the
                         * main content area using
                         * {@link LuCI.dom#append dom.append()}.
                         *
                         * This function is supposed to be overwritten by subclasses,
                         * the default implementation does nothing.
                         *
                         * @instance
                         * @abstract
                         * @memberof LuCI.view
                         * @param {*|null} load_results
                         * This function will receive the return value of the
                         * {@link LuCI.view#load view.load()} function as first
                         * argument.
                         *
                         * @returns {Node|Promise<Node>}
                         * Should return a DOM `Node` value or a `Promise` resolving
                         * to a `Node` value.
                         */
                        render: function() {},

                        /**
                         * The handleSave function is invoked when the user clicks
                         * the `Save` button in the page action footer.
                         *
                         * The default implementation should be sufficient for most
                         * views using {@link form#Map form.Map()} based forms - it
                         * will iterate all forms present in the view and invoke
                         * the {@link form#Map#save Map.save()} method on each form.
                         *
                         * Views not using `Map` instances or requiring other special
                         * logic should overwrite `handleSave()` with a custom
                         * implementation.
                         *
                         * To disable the `Save` page footer button, views extending
                         * this base class should overwrite the `handleSave` function
                         * with `null`.
                         *
                         * The invocation of this function is wrapped by
                         * `Promise.resolve()` so it may return Promises if needed.
                         *
                         * @instance
                         * @memberof LuCI.view
                         * @param {Event} ev
                         * The DOM event that triggered the function.
                         *
                         * @returns {*|Promise<*>}
                         * Any return values of this function are discarded, but
                         * passed through `Promise.resolve()` to ensure that any
                         * returned promise runs to completion before the button
                         * is reenabled.
                         */
                        handleSave: function(ev) {
                                var tasks = [];

                                document.getElementById('maincontent')
                                        .querySelectorAll('.cbi-map').forEach(function(map) {
                                                tasks.push(L.dom.callClassMethod(map, 'save'));
                                        });

                                return Promise.all(tasks);
                        },

                        /**
                         * The handleSaveApply function is invoked when the user clicks
                         * the `Save & Apply` button in the page action footer.
                         *
                         * The default implementation should be sufficient for most
                         * views using {@link form#Map form.Map()} based forms - it
                         * will first invoke
                         * {@link LuCI.view.handleSave view.handleSave()} and then
                         * call {@link ui#changes#apply ui.changes.apply()} to start the
                         * modal config apply and page reload flow.
                         *
                         * Views not using `Map` instances or requiring other special
                         * logic should overwrite `handleSaveApply()` with a custom
                         * implementation.
                         *
                         * To disable the `Save & Apply` page footer button, views
                         * extending this base class should overwrite the
                         * `handleSaveApply` function with `null`.
                         *
                         * The invocation of this function is wrapped by
                         * `Promise.resolve()` so it may return Promises if needed.
                         *
                         * @instance
                         * @memberof LuCI.view
                         * @param {Event} ev
                         * The DOM event that triggered the function.
                         *
                         * @returns {*|Promise<*>}
                         * Any return values of this function are discarded, but
                         * passed through `Promise.resolve()` to ensure that any
                         * returned promise runs to completion before the button
                         * is reenabled.
                         */
                        handleSaveApply: function(ev, mode) {
                                return this.handleSave(ev).then(function() {
                                        L.ui.changes.apply(mode == '0');
                                });
                        },

                        /**
                         * The handleReset function is invoked when the user clicks
                         * the `Reset` button in the page action footer.
                         *
                         * The default implementation should be sufficient for most
                         * views using {@link form#Map form.Map()} based forms - it
                         * will iterate all forms present in the view and invoke
                         * the {@link form#Map#save Map.reset()} method on each form.
                         *
                         * Views not using `Map` instances or requiring other special
                         * logic should overwrite `handleReset()` with a custom
                         * implementation.
                         *
                         * To disable the `Reset` page footer button, views extending
                         * this base class should overwrite the `handleReset` function
                         * with `null`.
                         *
                         * The invocation of this function is wrapped by
                         * `Promise.resolve()` so it may return Promises if needed.
                         *
                         * @instance
                         * @memberof LuCI.view
                         * @param {Event} ev
                         * The DOM event that triggered the function.
                         *
                         * @returns {*|Promise<*>}
                         * Any return values of this function are discarded, but
                         * passed through `Promise.resolve()` to ensure that any
                         * returned promise runs to completion before the button
                         * is reenabled.
                         */
                        handleReset: function(ev) {
                                var tasks = [];

                                document.getElementById('maincontent')
                                        .querySelectorAll('.cbi-map').forEach(function(map) {
                                                tasks.push(L.dom.callClassMethod(map, 'reset'));
                                        });

                                return Promise.all(tasks);
                        },

                        /**
                         * Renders a standard page action footer if any of the
                         * `handleSave()`, `handleSaveApply()` or `handleReset()`
                         * functions are defined.
                         *
                         * The default implementation should be sufficient for most
                         * views - it will render a standard page footer with action
                         * buttons labeled `Save`, `Save & Apply` and `Reset`
                         * triggering the `handleSave()`, `handleSaveApply()` and
                         * `handleReset()` functions respectively.
                         *
                         * When any of these `handle*()` functions is overwritten
                         * with `null` by a view extending this class, the
                         * corresponding button will not be rendered.
                         *
                         * @instance
                         * @memberof LuCI.view
                         * @returns {DocumentFragment}
                         * Returns a `DocumentFragment` containing the footer bar
                         * with buttons for each corresponding `handle*()` action
                         * or an empty `DocumentFragment` if all three `handle*()`
                         * methods are overwritten with `null`.
                         */
                        addFooter: function() {
                                var footer = E([]);

                                var saveApplyBtn = this.handleSaveApply ? new L.ui.ComboButton('0', {
                                        0: [ _('Save & Apply') ],
                                        1: [ _('Apply unchecked') ]
                                }, {
                                        classes: {
                                                0: 'cbi-button cbi-button-apply important',
                                                1: 'cbi-button cbi-button-negative important'
                                        },
                                        click: L.ui.createHandlerFn(this, 'handleSaveApply')
                                }).render() : E([]);

                                if (this.handleSaveApply || this.handleSave || this.handleReset) {
                                        footer.appendChild(E('div', { 'class': 'cbi-page-actions' }, [
                                                saveApplyBtn, ' ',
                                                this.handleSave ? E('button', {
                                                        'class': 'cbi-button cbi-button-save',
                                                        'click': L.ui.createHandlerFn(this, 'handleSave')
                                                }, [ _('Save') ]) : '', ' ',
                                                this.handleReset ? E('button', {
                                                        'class': 'cbi-button cbi-button-reset',
                                                        'click': L.ui.createHandlerFn(this, 'handleReset')
                                                }, [ _('Reset') ]) : ''
                                        ]));
                                }

                                return footer;
                        }
                })
        });

        /**
         * @class
         * @memberof LuCI
         * @deprecated
         * @classdesc
         *
         * The `LuCI.XHR` class is a legacy compatibility shim for the
         * functionality formerly provided by `xhr.js`. It is registered as global
         * `window.XHR` symbol for compatibility with legacy code.
         *
         * New code should use {@link LuCI.Request} instead to implement HTTP
         * request handling.
         */
        var XHR = Class.extend(/** @lends LuCI.XHR.prototype */ {
                __name__: 'LuCI.XHR',
                __init__: function() {
                        if (window.console && console.debug)
                                console.debug('Direct use XHR() is deprecated, please use L.Request instead');
                },

                _response: function(cb, res, json, duration) {
                        if (this.active)
                                cb(res, json, duration);
                        delete this.active;
                },

                /**
                 * This function is a legacy wrapper around
                 * {@link LuCI#get LuCI.get()}.
                 *
                 * @instance
                 * @deprecated
                 * @memberof LuCI.XHR
                 *
                 * @param {string} url
                 * The URL to request
                 *
                 * @param {Object} [data]
                 * Additional query string data
                 *
                 * @param {LuCI.requestCallbackFn} [callback]
                 * Callback function to invoke on completion
                 *
                 * @param {number} [timeout]
                 * Request timeout to use
                 *
                 * @return {Promise<null>}
                 */
                get: function(url, data, callback, timeout) {
                        this.active = true;
                        L.get(url, data, this._response.bind(this, callback), timeout);
                },

                /**
                 * This function is a legacy wrapper around
                 * {@link LuCI#post LuCI.post()}.
                 *
                 * @instance
                 * @deprecated
                 * @memberof LuCI.XHR
                 *
                 * @param {string} url
                 * The URL to request
                 *
                 * @param {Object} [data]
                 * Additional data to append to the request body.
                 *
                 * @param {LuCI.requestCallbackFn} [callback]
                 * Callback function to invoke on completion
                 *
                 * @param {number} [timeout]
                 * Request timeout to use
                 *
                 * @return {Promise<null>}
                 */
                post: function(url, data, callback, timeout) {
                        this.active = true;
                        L.post(url, data, this._response.bind(this, callback), timeout);
                },

                /**
                 * Cancels a running request.
                 *
                 * This function does not actually cancel the underlying
                 * `XMLHTTPRequest` request but it sets a flag which prevents the
                 * invocation of the callback function when the request eventually
                 * finishes or timed out.
                 *
                 * @instance
                 * @deprecated
                 * @memberof LuCI.XHR
                 */
                cancel: function() { delete this.active },

                /**
                 * Checks the running state of the request.
                 *
                 * @instance
                 * @deprecated
                 * @memberof LuCI.XHR
                 *
                 * @returns {boolean}
                 * Returns `true` if the request is still running or `false` if it
                 * already completed.
                 */
                busy: function() { return (this.active === true) },

                /**
                 * Ignored for backwards compatibility.
                 *
                 * This function does nothing.
                 *
                 * @instance
                 * @deprecated
                 * @memberof LuCI.XHR
                 */
                abort: function() {},

                /**
                 * Existing for backwards compatibility.
                 *
                 * This function simply throws an `InternalError` when invoked.
                 *
                 * @instance
                 * @deprecated
                 * @memberof LuCI.XHR
                 *
                 * @throws {InternalError}
                 * Throws an `InternalError` with the message `Not implemented`
                 * when invoked.
                 */
                send_form: function() { L.error('InternalError', 'Not implemented') },
        });

        XHR.get = function() { return window.L.get.apply(window.L, arguments) };
        XHR.post = function() { return window.L.post.apply(window.L, arguments) };
        XHR.poll = function() { return window.L.poll.apply(window.L, arguments) };
        XHR.stop = Request.poll.remove.bind(Request.poll);
        XHR.halt = Request.poll.stop.bind(Request.poll);
        XHR.run = Request.poll.start.bind(Request.poll);
        XHR.running = Request.poll.active.bind(Request.poll);

        window.XHR = XHR;
        window.LuCI = LuCI;
})(window, document);