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1.0.2 • Public • Published


Web port of the FCEUX Nintendo Entertainment System/Famicom (NES/FC) emulator. Powered by Emscripten.

Try it at


em-fceux enables the FCEUX emulator core feators on web browsers. The emulation runs at 60 FPS on modern computers, has low input latency and good audio quality. It also supports save states and battery-backed save RAM.

Additionally it has a new custom NTSC video signal and CRT TV emulation modes.


There are some modifications in FCEUX to make the code suitable for Emscripten. Primary addition is WebGL renderer which enables the use of shaders.

Supported FCEUX features:

  • Both NTSC and PAL system emulation.
  • All mappers supported by FCEUX.
  • Save states and battery-backed SRAM.
  • Speed throttling.
  • Support for two game controllers.
  • Zapper support.
  • Support for NES, ZIP and NSF file formats.

Unsupported FCEUX features:

  • New PPU emulation (old PPU emulation used for performance).
  • FDS disk system.
  • VS system.
  • Special peripherals (Family Keyboard, Mahjong controller, etc.)
  • Screenshots and movie recording.
  • Cheats, debug, TAS and Lua scripting features.

New features:

  • NTSC composite video emulation.
  • CRT TV emulation.





  1. Install and activate Emscripten 1.39.4 (upstream).
  2. Have python 2.7.x.
  3. Install scons.
  4. Run source to setup Emscripten env.
    • Note, this also sets npm to env.
  5. Run npm install.

Build for debug with npm run build:debug and for release with npm run build (results will be in dist/).

Building Shaders

You only need to rebuild the shaders when the shader sources in src/drivers/em/assets/shaders/ are changed. Do this with npm run build:shaders. This will download and build glsl-optimizer from source, and requires cmake and a C++ compiler.

Note, npm run build:shaders must be run before npm run build as the shaders are embedded in the output binary.

Browser Requirements

NTSC video signal and CRT TV Emulation Details

The NTSC signal emulation models the composite YIQ output. Separation of YIQ luminance (Y) and chrominance (IQ/UV) is done with a "1D comb filter" technique which reduces chroma fringing compared to band/low-pass filtering. Under the hood, YIQ to RGB conversion relies on a large lookup texture which is referenced in a fragment shader.


Authored by Valtteri "tsone" Heikkilä.

Please submit bugs and feature requests in the em-fceux issue tracker.


Licensed under GNU GPL 2.

This port if base on FCEUX 2.2.2 source code release.


npm i em-fceux

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