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WebAssembly.Instance

A WebAssembly.Instance object is a stateful, executable instance of a WebAssembly.Module. Instance objects contain all the Exported WebAssembly functions that allow calling into WebAssembly code from JavaScript.

Constructor

WebAssembly.Instance(): Creates a new Instance object.

Instance properties

Instance.prototype.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

The WebAssembly.Instance() constructor function can be called to synchronously instantiate a given WebAssembly.Module object, for example:

const importObject = {
  imports: {
    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 an Instance is asynchronously, for example using the WebAssembly.instantiateStreaming() function like this:

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

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

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

Specifications

Specification
WebAssembly JavaScript Interface: Exception Handling # instances

Browser compatibility

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	Deno	Node.js
`Instance`	57	16	52	No	44	11	57	57	52	43	11	7.0	1.0	8.0.0
`Instance`	57	16	52	No	44	11	57	57	52	43	11	7.0	1.0	8.0.0
`exports`	57	16	52	No	44	11	57	57	52	43	11	7.0	1.0	8.0.0