I put together a mobile-friendly version of a Javascript NES emulator for a hackathon [1], and I converted it to use the Web Audio API[2]. It works, but sounds very janky. I had to divide all of the integer audio samples into floating point values just so that they could be converted to integer values at some point later on. I also wanted to be able to use a gamepad for the emulator, but the last revision to the Gamepad API was a year ago[3], and browser support is pretty lacking[4]. I really like the idea of browser emulation because native emulators are banned from the App Store, but the web APIs are just not there yet.

Side note: If anyone wants to take over webNES and make it awesome, free free to message me

[1] http://webn.es

[2] https://github.com/conradev/jsnes/commit/6b0ef8d5b5d0a7b17e6...

[3] https://dvcs.w3.org/hg/gamepad/raw-file/default/gamepad.html

[4] http://caniuse.com/#feat=gamepad