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    1.4.0 • Public • Published

    WebAssembly Feature Detection

    A small library to detect which features of WebAssembly are supported.

    • Runs in all major browsers
    • Runs in Node
    • Provided as an ES6 module, CommonJS and UMD module.
    • CSP compatible
    • Only ~640B gzipped


    npm install -g wasm-feature-detect


    <script type="module">
      import { simd } from "";
      simd().then(simdSupported => {
        if (simdSupported) {
          /* SIMD support */
        } else {
          /* No SIMD support */

    If required, there’s also a UMD version

    <script src=""></script>
      wasmFeatureDetect.simd().then(/* same as above */);


    All detectors return a Promise<bool>.

    Function Proposal
    bigInt() BigInt integration
    bulkMemory() Bulk memory operations
    exceptions() Exception handling
    extendedConst() Extented Const Expressesions
    memory64() Memory64
    multiValue() Multi-value
    mutableGlobals() Importable/Exportable mutable globals
    referenceTypes() Reference Types
    relaxedSimd() Relaxed SIMD
    saturatedFloatToInt() Non-trapping float-to-int conversions
    signExtensions() Sign-extension operators
    simd() Fixed-Width SIMD
    streamingCompilation() Streaming Compilation
    tailCall() Tail call
    threads() Threads

    Why are all the tests async?

    The technical reason is that some tests might have to be augmented to be asynchronous in the future. For example, Firefox is planning to make a change that would require a postMessage call to detect SABs, which are required for threads.

    The other reason is that you should be using WebAssembly.compile, WebAssembly.instantiate, or their streaming versions WebAssembly.compileStreaming and WebAssembly.instantiateStreaming, which are all asynchronous. You should already be prepared for asynchronous code when using WebAssembly!


    If you want to contribute a new feature test, all you need to do is create a new folder in src/detectors and it will be automatically picked up. The folder may contain a module.wat file, which will be compiled using wabt.js.

    ;; Name: <Name of the feature for the README>
    ;; Proposal: <Link to the proposal’s explainer/repo>
    ;; Features: <Space-separated list of WasmFeatures from wabt.js>
      ;; More WAT code here

    The folder can also contain an optional index.js file, whose default export must be an async function. This function can do additional testing in JavaScript and must return a boolean. See the “threads” detector as an example. It must contain at least one of module.wat or index.js.

    License Apache-2.0




    npm i wasm-feature-detect

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    Unpacked Size

    27.4 kB

    Total Files


    Last publish


    • rreverser
    • surma