XNES – Experimental JavaScript Super Nintendo emulators ( Source).
Nezulator – A NES emulator in JavaScript.
JSNES – A JavaScript NES emulator ( Source).
IodineGBA – A GameBoy Advance emulator written entirely in JavaScript ( Source).
GameBoy Online – JavaScript GameBoy Color emulator ( Source).
GBA.js – Game Boy Advance in the Browser ( Source).
CycloaJS – JavaScript NES Emulator ( Source).
1964js – JavaScript port of the 1964 N64 emulator for Windows.
pdp11-js – PDP-11 emulator with UNIX V6.
PDP-11 Emulator – A JavaScript PDP-11 emulator.
VICE.js – Versatile Commodore Emulator for JavaScript ( Source).
VIC-20 Emulator – JavaScript VIC-20 emulator.
SAE – Scripted Amiga Emulator ( Source).
JSC64 – Commodore 64 emulator written in JavaScript ( Source).
jsA8E – JavaScript version of the A8E Atari 800 XL Emulator.
EstyJS – A pretty fast and functional JavaScript Atari ST emulator ( Source).
Apple2JS – A JavaScript emulator for the Apple II.
a2 – A fast, WebGL optimized Apple ][+ emulator.
Apple IIjs – An Apple ][ Emulator in JavaScript.
Roland – An Amstrad CPC emulator written in JavaScript.
CPCBox – Amstrad CPC emulator in JavaScript.
I’ve pasted the list below, but special thanks to Frederic Cambus who compiled the list. There’s a great list over at Github of about 50 emulators written in Javascript.