WebAssembly.instantiateStreaming()

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The WebAssembly.instantiateStreaming() function compiles and instantiates a WebAssembly module directly from a streamed underlying source.

Syntax

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

Parameters

source
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:

Exceptions

Examples

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.

Specifications

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 Yes58 No47 ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support6161 Yes158 No ? ?

1. This feature is behind the Experimental JavaScript Features preference.

See also

Document Tags and Contributors

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