audventure/scripts/audio.js

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();

function loadSound(url) {
  return fetch(url)
    .then(response => response.arrayBuffer())
    .then(buffer => audioCtx.decodeAudioData(buffer))
    .then(audio => new Sound(audio, url));
}

function SFXManager() {
  this.soundMap = {}
}

SFXManager.prototype.loadSound = function(name, url) {
  var self = this;
  return loadSound(url).then(sound => {
    self.soundMap[name] = sound;
  })
}

SFXManager.prototype.play = function(name) {
  this.soundMap[name].play();
}

SFXManager.prototype.unloadSound = function(name) {
  delete this.soundMap[name];
}

function Sound(buffer, url) {
  this.buffer = buffer;
  this.url = url;
  this._target = audioCtx.destination;
  this._source = null;
  this._playStartTime = 0;
  this._timeToStartFrom = 0;
  this._playing = false;
}

Sound.prototype.setTarget = function(target) {
  this._target = target;
  if(this._playing) {
    this.pause();
    this.resume();
  }
}

Sound.prototype._start = function(offset) {
  this._source = audioCtx.createBufferSource();
  this._source.buffer = this.buffer;
  this._source.connect(this._target);
  this._source.onended = function() {
    this._playing = false;
    this._timeToStartFrom = 0;
  }.bind(this);
  this._playStartTime = audioCtx.currentTime;
  this._timeToStartFrom = offset;
  this._playing = true;
  this._source.start(0, this._timeToStartFrom);
}

Sound.prototype.play = function() {
  if(this._playing) {
    this.pause();
  }
  this._start(0);
}

Sound.prototype.resume = function() {
  this._start(this._timeToStartFrom);
}

Sound.prototype.pause = function() {
  // in case the sound has not been played yet
  if(this._source == null) return;

  this._playing = false;
  this._source.onended = null;
  this._source.stop();
  this._source.disconnect();
  var elapsedTime = this._timeToStartFrom + audioCtx.currentTime - this._playStartTime;
  this._timeToStartFrom = elapsedTime;
}

var sfxManager = new SFXManager();