The WebAssembly.instantiateStreaming() function compiles and instantiates a WebAssembly module directly from a streamed underlying source. This is the most efficient, optimized way to load wasm code.


Promise<ResultObject> WebAssembly.instantiateStreaming(source, importObject);


A Response object or a promise that will fulfill with one, representing the underlying source of a .wasm module you want to stream, compile, and instantiate.
importObject Optional
An object containing the values to be imported into the newly-created Instance, such as functions or WebAssembly.Memory objects. There must be one matching property for each declared import of the compiled module or else a WebAssembly.LinkError is thrown.

Return value

A Promise that resolves to a ResultObject which contains two fields:



Instantiating streaming

The following example (see our instantiate-streaming.html demo on GitHub, and view it live also) directly streams a .wasm module from an underlying source then compiles and instantiates it, the promise fulfilling with a ResultObject. Because the instantiateStreaming()  function accepts a promise for a Response object, you can directly pass it a WindowOrWorkerGlobalScope.fetch() call, and it will pass the response into the function when it fulfills.

var importObject = { imports: { imported_func: arg => console.log(arg) } };

WebAssembly.instantiateStreaming(fetch('simple.wasm'), importObject)
.then(obj => obj.instance.exports.exported_func());

The ResultObject's instance member is then accessed, and the contained exported function invoked.

Note: For this to work, .wasm files should be returned with an application/wasm MIME type by the server.


WebAssembly features for web embedding
The definition of 'instantiateStreaming()' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
instantiateStreamingChrome Full support 61Edge Full support 16Firefox Full support 58IE No support NoOpera Full support 47Safari No support NoWebView Android Full support 61Chrome Android Full support 61Firefox Android Full support 58Opera Android Full support 45Safari iOS No support NoSamsung Internet Android Full support 8.0nodejs No support No


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See also