stockfish.wasm

stockfish.wasm

WebAssembly port of the strong chess engine Stockfish. See it in action on https://lichess.org/analysis.

Requirements

Uses the latest WebAssembly threading proposal.

• Available as an Origin Trial in Chrome 70.
• Behind a flag since Chrome 70: chrome://flags/#enable-webassembly-threads
• Behind a flag in Firefox Nightly: javascript.options.shared_memory in about:config.

See stockfish.js for a more portable but single-threaded version.

Feature detection:

typeof WebAssembly === 'object' &&
WebAssembly.validate(Uint8Array.of(0x0, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00)) &&
typeof SharedArrayBuffer === 'function' &&
new WebAssembly.Memory({shared: true, initial: 8, maximum: 8}).buffer instanceof SharedArrayBuffer

Limitations

• Maximum number of threads determined at compile time (currently 8).
• Maximum size of hashtable determined at compile time (currently 16 MB).
• No Syzygy tablebase support.
• Exposed as a global variable in JavaScript (window.Module), only one instance per site.

Building

Assuming em++ is available:

cd src
make ARCH=wasm build

Usage

Requires stockfish.js, stockfish.wasm, stockfish.js.mem and pthread-main.js to be served from the same directory.

<script src="stockfish.js"></script>
<script>
Module.addMessageListener(function (line) {
  console.log(line);
});

Module.postMessage('uci');
</script>

License

Thanks to the Stockfish team for sharing the engine under the GPL3.