michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: "use strict";
michael@0: 
michael@0: module.metadata = {
michael@0:   "stability": "unstable"
michael@0: };
michael@0: 
michael@0: // Utility function that returns copy of the given `text` with last character
michael@0: // removed if it is `"s"`.
michael@0: function singularify(text) {
michael@0:   return text[text.length - 1] === "s" ? text.substr(0, text.length - 1) : text;
michael@0: }
michael@0: 
michael@0: // Utility function that takes event type, argument is passed to
michael@0: // `document.createEvent` and returns name of the initializer method of the
michael@0: // given event. Please note that there are some event types whose initializer
michael@0: // methods can't be guessed by this function. For more details see following
michael@0: // link: https://developer.mozilla.org/En/DOM/Document.createEvent
michael@0: function getInitializerName(category) {
michael@0:   return "init" + singularify(category);
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Registers an event `listener` on a given `element`, that will be called
michael@0:  * when events of specified `type` is dispatched on the `element`.
michael@0:  * @param {Element} element
michael@0:  *    Dom element to register listener on.
michael@0:  * @param {String} type
michael@0:  *    A string representing the
michael@0:  *    [event type](https://developer.mozilla.org/en/DOM/event.type) to
michael@0:  *    listen for.
michael@0:  * @param {Function} listener
michael@0:  *    Function that is called whenever an event of the specified `type` 
michael@0:  *    occurs.
michael@0:  * @param {Boolean} capture
michael@0:  *    If true, indicates that the user wishes to initiate capture. After
michael@0:  *    initiating capture, all events of the specified type will be dispatched
michael@0:  *    to the registered listener before being dispatched to any `EventTarget`s
michael@0:  *    beneath it in the DOM tree. Events which are bubbling upward through
michael@0:  *    the tree will not trigger a listener designated to use capture.
michael@0:  *    See [DOM Level 3 Events](http://www.w3.org/TR/DOM-Level-3-Events/#event-flow)
michael@0:  *    for a detailed explanation.
michael@0:  */
michael@0: function on(element, type, listener, capture) {
michael@0:   // `capture` defaults to `false`.
michael@0:   capture = capture || false;
michael@0:   element.addEventListener(type, listener, capture);
michael@0: }
michael@0: exports.on = on;
michael@0: 
michael@0: /**
michael@0:  * Registers an event `listener` on a given `element`, that will be called
michael@0:  * only once, next time event of specified `type` is dispatched on the
michael@0:  * `element`.
michael@0:  * @param {Element} element
michael@0:  *    Dom element to register listener on.
michael@0:  * @param {String} type
michael@0:  *    A string representing the
michael@0:  *    [event type](https://developer.mozilla.org/en/DOM/event.type) to
michael@0:  *    listen for.
michael@0:  * @param {Function} listener
michael@0:  *    Function that is called whenever an event of the specified `type` 
michael@0:  *    occurs.
michael@0:  * @param {Boolean} capture
michael@0:  *    If true, indicates that the user wishes to initiate capture. After
michael@0:  *    initiating capture, all events of the specified type will be dispatched
michael@0:  *    to the registered listener before being dispatched to any `EventTarget`s
michael@0:  *    beneath it in the DOM tree. Events which are bubbling upward through
michael@0:  *    the tree will not trigger a listener designated to use capture.
michael@0:  *    See [DOM Level 3 Events](http://www.w3.org/TR/DOM-Level-3-Events/#event-flow)
michael@0:  *    for a detailed explanation.
michael@0:  */
michael@0: function once(element, type, listener, capture) {
michael@0:   on(element, type, function selfRemovableListener(event) {
michael@0:     removeListener(element, type, selfRemovableListener, capture);
michael@0:     listener.apply(this, arguments);
michael@0:   }, capture);
michael@0: }
michael@0: exports.once = once;
michael@0: 
michael@0: /**
michael@0:  * Unregisters an event `listener` on a given `element` for the events of the
michael@0:  * specified `type`.
michael@0:  *
michael@0:  * @param {Element} element
michael@0:  *    Dom element to unregister listener from.
michael@0:  * @param {String} type
michael@0:  *    A string representing the
michael@0:  *    [event type](https://developer.mozilla.org/en/DOM/event.type) to
michael@0:  *    listen for.
michael@0:  * @param {Function} listener
michael@0:  *    Function that is called whenever an event of the specified `type` 
michael@0:  *    occurs.
michael@0:  * @param {Boolean} capture
michael@0:  *    If true, indicates that the user wishes to initiate capture. After
michael@0:  *    initiating capture, all events of the specified type will be dispatched
michael@0:  *    to the registered listener before being dispatched to any `EventTarget`s
michael@0:  *    beneath it in the DOM tree. Events which are bubbling upward through
michael@0:  *    the tree will not trigger a listener designated to use capture.
michael@0:  *    See [DOM Level 3 Events](http://www.w3.org/TR/DOM-Level-3-Events/#event-flow)
michael@0:  *    for a detailed explanation.
michael@0:  */
michael@0: function removeListener(element, type, listener, capture) {
michael@0:   element.removeEventListener(type, listener, capture);
michael@0: }
michael@0: exports.removeListener = removeListener;
michael@0: 
michael@0: /**
michael@0:  * Emits event of the specified `type` and `category` on the given `element`.
michael@0:  * Specified `settings` are used to initialize event before dispatching it.
michael@0:  * @param {Element} element
michael@0:  *    Dom element to dispatch event on.
michael@0:  * @param {String} type
michael@0:  *    A string representing the
michael@0:  *    [event type](https://developer.mozilla.org/en/DOM/event.type).
michael@0:  * @param {Object} options
michael@0:  *    Options object containing following properties:
michael@0:  *    - `category`: String passed to the `document.createEvent`. Option is
michael@0:  *      optional and defaults to "UIEvents".
michael@0:  *    - `initializer`: If passed it will be used as name of the method used
michael@0:  *      to initialize event. If omitted name will be generated from the
michael@0:  *      `category` field by prefixing it with `"init"` and removing last
michael@0:  *      character if it matches `"s"`.
michael@0:  *    - `settings`: Array of settings that are forwarded to the event
michael@0:  *      initializer after firs `type` argument.
michael@0:  * @see https://developer.mozilla.org/En/DOM/Document.createEvent
michael@0:  */
michael@0: function emit(element, type, { category, initializer, settings }) {
michael@0:   category = category || "UIEvents";
michael@0:   initializer = initializer || getInitializerName(category);
michael@0:   let document = element.ownerDocument;
michael@0:   let event = document.createEvent(category);
michael@0:   event[initializer].apply(event, [type].concat(settings));
michael@0:   element.dispatchEvent(event);
michael@0: };
michael@0: exports.emit = emit;