WebAssembly.Instance

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨October 2017⁩.

AWebAssembly.Instance object is a stateful, executable instance of aWebAssembly.Module.Instance objects contain all theExported WebAssembly functions that allow calling into WebAssembly code from JavaScript.

Constructor

WebAssembly.Instance(): Creates a newInstance object.

Instance properties

exports: Returns an object containing as its members all the functions exported from the WebAssembly module instance, to allow them to be accessed and used by JavaScript. Read-only.

Examples

Synchronously instantiating a WebAssembly module

TheWebAssembly.Instance() constructor function can be called to synchronously instantiate a givenWebAssembly.Module object, for example:

const importObject = {  my_namespace: {    imported_func(arg) {      console.log(arg);    },  },};fetch("simple.wasm")  .then((response) => response.arrayBuffer())  .then((bytes) => {    const mod = new WebAssembly.Module(bytes);    const instance = new WebAssembly.Instance(mod, importObject);    instance.exports.exported_func();  });

The preferred way to get anInstance is asynchronously, for example using theWebAssembly.instantiateStreaming() function like this:

const importObject = {  my_namespace: {    imported_func(arg) {      console.log(arg);    },  },};WebAssembly.instantiateStreaming(fetch("simple.wasm"), importObject).then(  (obj) => obj.instance.exports.exported_func(),);

This also demonstrates how theexports property is used to access exported functions.