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: function(arg) {
      console.log(arg);
    }
  }
};

fetch('simple.wasm').then(response =>
  response.arrayBuffer()
).then(bytes => {
  let mod = new WebAssembly.Module(bytes);
  let 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: function(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

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
Instance
57
16
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No
44
11
57
57
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43
11
7.0
Instance
57
16
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No
44
11
57
57
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43
11
7.0
exports
57
16
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No
44
11
57
57
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43
11
7.0

See also

© 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance