via http://www.emucr.com/

GameBoy Online (2013/11/09) is released. GameBoy Online is a Game Boy and GameBoy Color emulator written in Javascript. It strives to be efficient and try to have a perfect compatibility. Currently the execution speed is not optimal even on browsers. For example on Chrome, which is nevertheless deemed to run Javascript faster on a PC running Windows 7 64-bit version with a double heart 2 CPUs at 2.2 GHz, games run at normal speed but almost skipping some frames.

The sound production is still experimental and rather poor quality. The video portion is by HTML5 or by creating images with BMP string URI. State backups are implemented using the object window.localStorage and are serialized / deserialized JSON. Ditto for backup SRAM.

GameBoy Online Changelog:
- more settings twiddling
- clamp adjustment for buffer under-runs
limits audio buffering per iteration so an iteration doesn't block the
main thread too long in case there was a large underrun.
- adding retest notes
- clarify
- Updating readme
Firefox killed low latency audio in nightly it seems

https://github.com/grantgalitz/GameBoy-Online