StartAudioContext.js

/**
 *  StartAudioContext.js
 *  @author Yotam Mann
 *  @license http://opensource.org/licenses/MIT MIT License
 *  @copyright 2016 Yotam Mann
 */
(function (root, factory) {
	if (typeof define === "function" && define.amd) {
		define([], factory)
	 } else if (typeof module === "object" && module.exports) {
        module.exports = factory()
	} else {
		root.StartAudioContext = factory()
  }
}(this, function () {

	//TAP LISTENER/////////////////////////////////////////////////////////////

	/**
	 * @class  Listens for non-dragging tap ends on the given element
	 * @param {Element} element
	 * @internal
	 */
	var TapListener = function(element, context){

		this._dragged = false

		this._element = element

		this._bindedMove = this._moved.bind(this)
		this._bindedEnd = this._ended.bind(this, context)

		element.addEventListener("touchstart", this._bindedEnd)
		element.addEventListener("touchmove", this._bindedMove)
		element.addEventListener("touchend", this._bindedEnd)
		element.addEventListener("mouseup", this._bindedEnd)
	}

	/**
	 * drag move event
	 */
	TapListener.prototype._moved = function(e){
		this._dragged = true
	};

	/**
	 * tap ended listener
	 */
	TapListener.prototype._ended = function(context){
		if (!this._dragged){
			startContext(context)
		}
		this._dragged = false
	};

	/**
	 * remove all the bound events
	 */
	TapListener.prototype.dispose = function(){
		this._element.removeEventListener("touchstart", this._bindedEnd)
		this._element.removeEventListener("touchmove", this._bindedMove)
		this._element.removeEventListener("touchend", this._bindedEnd)
		this._element.removeEventListener("mouseup", this._bindedEnd)
		this._bindedMove = null
		this._bindedEnd = null
		this._element = null
	};

	//END TAP LISTENER/////////////////////////////////////////////////////////

	/**
	 * Plays a silent sound and also invoke the "resume" method
	 * @param {AudioContext} context
	 * @private
	 */
	function startContext(context){
		// this accomplishes the iOS specific requirement
		var buffer = context.createBuffer(1, 1, context.sampleRate)
		var source = context.createBufferSource()
		source.buffer = buffer
		source.connect(context.destination)
		source.start(0)

		// resume the audio context
		if (context.resume){
			context.resume()
		}
	}

	/**
	 * Returns true if the audio context is started
	 * @param  {AudioContext}  context
	 * @return {Boolean}
	 * @private
	 */
	function isStarted(context){
		 return context.state === "running"
	}

	/**
	 * Invokes the callback as soon as the AudioContext
	 * is started
	 * @param  {AudioContext}   context
	 * @param  {Function} callback
	 */
	function onStarted(context, callback){

		function checkLoop(){
			if (isStarted(context)){
				callback()
			} else {
				requestAnimationFrame(checkLoop)
				if (context.resume){
					context.resume()
				}
			}
		}

		if (isStarted(context)){
			callback()
		} else {
			checkLoop()
		}
	}

	/**
	 * Add a tap listener to the audio context
	 * @param  {Array|Element|String|jQuery} element
	 * @param {Array} tapListeners
	 */
	function bindTapListener(element, tapListeners, context){
		if (Array.isArray(element) || (NodeList && element instanceof NodeList)){
			for (var i = 0; i < element.length; i++){
				bindTapListener(element[i], tapListeners, context)
			}
		} else if (typeof element === "string"){
			bindTapListener(document.querySelectorAll(element), tapListeners, context)
		} else if (element.jquery && typeof element.toArray === "function"){
			bindTapListener(element.toArray(), tapListeners, context)
		} else if (Element && element instanceof Element){
			//if it's an element, create a TapListener
			var tap = new TapListener(element, context)
			tapListeners.push(tap)
		} 
	}

	/**
	 * @param {AudioContext} context The AudioContext to start.
	 * @param {Array|String|Element|jQuery=} elements For iOS, the list of elements
	 *                                               to bind tap event listeners
	 *                                               which will start the AudioContext. If
	 *                                               no elements are given, it will bind
	 *                                               to the document.body.
	 * @param {Function=} callback The callback to invoke when the AudioContext is started.
	 * @return {Promise} The promise is invoked when the AudioContext
	 *                       is started.
	 */
	function StartAudioContext(context, elements, callback){

		//the promise is invoked when the AudioContext is started
		var promise = new Promise(function(success) {
			onStarted(context, success)
		})

		// The TapListeners bound to the elements
		var tapListeners = []

		// add all the tap listeners
		if (!elements){
			elements = document.body
		}
		bindTapListener(elements, tapListeners, context)

		//dispose all these tap listeners when the context is started
		promise.then(function(){
			for (var i = 0; i < tapListeners.length; i++){
				tapListeners[i].dispose()
			}
			tapListeners = null

			if (callback){
				callback()
			}
		})

		return promise
	}

	return StartAudioContext
}))