webaudio.js

// Begin by creating an audioContext object. Safari still requires
// us to use webkitAudioContext instead of AudioContext.
let audioContext = new (this.AudioContext||this.webkitAudioContext)();

// Define the base sound as a combination of three pure sine waves
let notes = [ 293.7, 370.0, 440.0 ]; // D major chord: D, F# and A

// Create oscillator nodes for each of the notes we want to play
let oscillators = notes.map(note => {
    let o = audioContext.createOscillator();
    o.frequency.value = note;
    return o;
});

// Shape the sound by controlling its volume over time.
// Starting at time 0 quickly ramp up to full volume.
// Then starting at time 0.1 slowly ramp down to 0.
let volumeControl = audioContext.createGain();
volumeControl.gain.setTargetAtTime(1, 0.0, 0.02);
volumeControl.gain.setTargetAtTime(0, 0.1, 0.2);

// We're going to send the sound to the default destination:
// the user's speakers
let speakers = audioContext.destination;

// Connect each of the source notes to the volume control
oscillators.forEach(o => o.connect(volumeControl));

// And connect the output of the volume control to the speakers.
volumeControl.connect(speakers);

// Now start playing the sounds and let them run for 1.25 seconds.
let startTime = audioContext.currentTime;
let stopTime = startTime + 1.25;
oscillators.forEach(o => {
    o.start(startTime);
    o.stop(stopTime);
});

// If we want to create a sequence of sounds we can use event handlers
oscillators[0].addEventListener("ended", () => {
    // This event handler is invoked when the note stops playing
});