There’s a great list over at Github of about 50 emulators written in Javascript.
I’ve pasted the list below, but special thanks to Frederic Cambus who compiled the list.
Amstrad
Apple
- Apple IIjs – An Apple ][ Emulator in JavaScript
- a2 – A fast, WebGL optimized Apple ][+ emulator.
- Apple2JS – A JavaScript emulator for the Apple II
Atari
- EstyJS – A pretty fast and functional JavaScript Atari ST emulator (Source)
- jsA8E – JavaScript version of the A8E Atari 800 XL Emulator
Commodore
- JSC64 – Commodore 64 emulator written in JavaScript (Source)
- SAE – Scripted Amiga Emulator (Source)
- VIC-20 Emulator – JavaScript VIC-20 emulator
- VICE.js – Versatile Commodore Emulator for JavaScript (Source)
DEC
- PDP-11 Emulator – A JavaScript PDP-11 emulator
- pdp11-js – PDP-11 emulator with UNIX V6
Nintendo
- 1964js – JavaScript port of the 1964 N64 emulator for Windows
- CycloaJS – JavaScript NES Emulator (Source)
- GBA.js – Game Boy Advance in the Browser (Source)
- GameBoy Online – JavaScript GameBoy Color emulator (Source)
- IodineGBA – A GameBoy Advance emulator written entirely in JavaScript (Source)
- JSNES – A JavaScript NES emulator (Source)
- Nezulator – A NES emulator in JavaScript
- XNES – Experimental JavaScript Super Nintendo emulators (Source)
- fam – JavaScript NES emulator (Source)
- jsGB – A GameBoy emulator in JavaScript (Source)
- mupen64plus – A port of the popular Nintendo 64 emulator for the Web (Source)
- n64js – An N64 emulator in JavaScript (Source)
PC Emulators
- JS/Linux – JavaScript PC emulator
- JsDOSBox – JavaScript PC DOS emulator (Source)
- PCjs – IBM PC Model 5150 emulator
- Virtual x86 – An x86 emulator written in JavaScript (Source)
- jemul8 – An object-oriented JavaScript x86 emulator for Node.js and the Browser (Source)
- jsbochs – Bochs PC emulator for the Browser (Source)
Sega
- jsSMS – JavaScript Sega Master System & Game Gear emulator (Source)
- Miracle – Sega Master System emulator (Source)
Sinclair
- JSSpeccy – A ZX Spectrum emulator in JavaScript (Source)
- Qaop/JS – ZX Spectrum emulator
- ZX80 Emulator – JavaScript ZX80 Emulator
- jBacteria – The smallest JavaScript Spectrum emulator
Tandy
- MC-10 Emulator – Emulator for the TRS-80 MC-10 microcomputer
- jTandy – Another JavaScript TRS-80 emulator
Multi-system Emulators
- JSMESS – The JavaScript MESS (Multi Emulator Super System) (Source)
- PCE – PC emulators in JavaScript (Atari ST, IBM PC 5150, Macintosh, RC759 Piccoline)
- RetroArch – JavaScript port of RetroArch (bundles Gambatte (Gameboy), Genesis Plus GX, Handy (Lynx), Snes9x Next, VBA Next (GameBoy Advance), Tyrquake and FinalBurn Alpha)
Miscellaneous
- Burroughs B5500 emulator – Burroughs B5500 emulator in JavaScript (Source)
- Compucolor II Emulator – JavaScript Compucolor II Emulator
- ElkJS – JavaScript based Acorn Electron emulator (Source)
- Intel 8080 CPU Emulator – Emulates a minimal Intel 8080 Microcomputer that runs CP/M
- JSBeeb – JavaScript BBC Micro emulator (Source)
- JsPspEmu – JavaScript PSP emulator (Source)
- NanoWasp – A MicroBee emulator
- TI-92 Plus emulator – JavaScript emulator for the TI-92 Plus
- jor1k – OpenRISC OR1K JavaScript emulator running Linux with network support (Source)
- jsMSX – The first MSX emulator 100% written in JavaScript
- jslm32 – JavaScript LatticeMico32 emulator running Linux (Source)
- jupiler – Jupiter Ace emulator written in JavaScript
You can find the full list this Github link.