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:



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.


Specification Status Comment
WebAssembly features for web embedding
The definition of 'instantiateStreaming()' in that specification.
Draft Initial draft definition.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support61 No58 No47 No
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support6161 No58 ? No No

See also

Document Tags and Contributors

 Contributors to this page: chrisdavidmills
 Last updated by: chrisdavidmills,