I used Tone.js to create my music theory website https://www.lightnote.co/

Using recordings from my guitar (of each and every note) I was able to build an interactive fretboard that could play guitar tabs/chords. Also the Transport API made it simple to build a drum looping machine very quickly.

Ableton has built something similar, also using Tone.js: https://learningmusic.ableton.com/make-beats/make-beats.html

Performance on mobile leaves a lot to be desired. I found there was considerable lag.