Sound JS
A Javascript library for working with Audio. Features a simple interface as the front end to multiple audio APIs via a plugin model. Currently supports HTML5 Audio & Flash.
Audio5js
The HTML5 Audio Compatibility Layer
Pizzicato
Library to simplify the way you create and manipulate sounds with the Web Audio API.
Timbre.js
JavaScript library for objective sound programming
Howler.js
Javascript audio library for the modern web.
Sound Manager 2
A JavaScript Sound API supporting MP3, MPEG4 and HTML5 audio + (experimental) RTMP, providing reliable cross-browser/platform audio control in as little as 10 KB. BSD licensed.
Tone.js
A Web Audio framework for making interactive music in the browser.
Buzz
Buzz is a small but powerful Javascript library that allows you to easily take advantage of the new HTML5 audio element. It tries to degrade gracefully on non-modern browsers.
Alpha Tab
alphaTab is a cross platform music notation and guitar tablature rendering library.
Speak.js
Text-to-Speech in JavaScript using eSpeak
Teoria
A JavaScript music theory framework.