Tone.js/Tone/shim/AudioContext.js

import Tone from "../core/Tone";
import "../shim/OfflineAudioContext";

if (Tone.supported){
	if (!Tone.global.hasOwnProperty("AudioContext") && Tone.global.hasOwnProperty("webkitAudioContext")){
		Tone.global.AudioContext = Tone.global.webkitAudioContext;
	}

	//not functionally equivalent, but only an API placeholder
	if (!AudioContext.prototype.close){
		AudioContext.prototype.close = function(){
			if (Tone.isFunction(this.suspend)){
				this.suspend();
			}
			return Promise.resolve();
		};
	}

	//not functionally equivalent
	if (!AudioContext.prototype.resume){
		AudioContext.prototype.resume = function(){
			//play some silent audio to jumpstart the context
			var buffer = this.createBuffer(1, 1, this.sampleRate);
			var source = this.createBufferSource();
			source.buffer = buffer;
			source.connect(this.destination);
			source.start(0);
			return Promise.resolve();
		};
	}

	//createGain
	if (!AudioContext.prototype.createGain && AudioContext.prototype.createGainNode){
		AudioContext.prototype.createGain = AudioContext.prototype.createGainNode;
	}

	//createDelay
	if (!AudioContext.prototype.createDelay && AudioContext.prototype.createDelayNode){
		AudioContext.prototype.createDelay = AudioContext.prototype.createDelayNode;
	}

	//test decodeAudioData returns a promise
	// https://github.com/mohayonao/web-audio-api-shim/blob/master/src/AudioContext.js
	// MIT License (c) 2015 @mohayonao
	var decodeAudioDataPromise = false;
	var offlineContext = new OfflineAudioContext(1, 1, 44100);
	var audioData = new Uint32Array([1179011410, 48, 1163280727, 544501094, 16, 131073, 44100, 176400, 1048580, 1635017060, 8, 0, 0, 0, 0]).buffer;
	try {
		var ret = offlineContext.decodeAudioData(audioData);
		if (ret && Tone.isFunction(ret.then)){
			decodeAudioDataPromise = true;
		}
	} catch (e){
		decodeAudioDataPromise = false;
	}

	if (!decodeAudioDataPromise){
		AudioContext.prototype._native_decodeAudioData = AudioContext.prototype.decodeAudioData;
		AudioContext.prototype.decodeAudioData = function(audioData){
			return new Promise(function(success, error){
				this._native_decodeAudioData(audioData, success, error);
			}.bind(this));
		};
	}
}