js-audio contains some helpers for working with audio files in JavaScript. These are mostly experiments or proof-of-concepts.
mp3.js parses (not decodes) MP3. This allows you to split MP3 files on logical frames.
id3.js reads ID3 tags from MP3 files, including album artwork.
wave.js extracts chunks of wave files as AudioBuffers, and generates wave files (blobs). For reading wave files, David Lindkvist’s wav.js looks better.