AccuracyCoin comparison with the original as of Mar 12, 2026: (left nesjs, right znes)
A continuation of angelo-wf's NesJS project, written for the browser in JavaScript.
The CPU has almost all instructions emulated, but it is not cycle-accurate (and doesn't emulate the 'unstable' undocumented instructions). The PPU has full background and sprite rendering, but it is also not cycle-accurate. The APU emulates all 5 channels, but it is again not fully accurate. There are also some other inaccuracies (with OAM-DMA and such). Most games however seem to run fine (except the known broken games listed below).
Standard controllers 1 and 2 are emulated.
Supports mapper 0 (NROM), 1 (MMC1), 2 (UxROM), 3 (CNROM), 4 (MMC3) and 7 (AxROM). The MMC3's IRQ emulation is not really accurate though.
There is support for both save states and battery saves.
These are games that are known to crash/freeze. Games with only (minor) graphical problems are not listed. Almost all of those cases (and most of these cases as well) come down to the emulator not being cycle accurate.
- Battletoads
- Freezes when starting stage 2
- Battletoads and Double Dragon
- Freezes semi-randomly during stage 1
- Adventure of Lolo 3 (USA)
- Freezes when entering level 1
- Adventure of Lolo 2 (USA) / Adventure of Lolo (J)
- Freezes after HAI / copyright-screen
- MS. Pac-Man (Tengen)
- Freezes on boot (grey screen)
- Bill & Ted's Excellent Adventure
- Freezes on boot (grey screen)
- Huge Insect
- Freezes on boot (grey screen)
- Vegas Dream
- Freezes on boot (screen filled with single repeating tile)
- GI Joe - A Real American Hero
- Freezes on boot (grey screen)
- GI Joe - The Atlantic Factor
- Freezes on boot (black screen)
Thanks to the resources at the nesdev wiki and the nesdev forums for the test roms, documentation and some code snippets used for this.
Uses the zip.js library for zipped rom loading support.
Licensed under the MIT License. See LICENSE.txt for details.