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WebAssembly.instance.Instance

The WebAssembly.Instance() constructor creates a new Instance object which is a stateful, executable instance of a WebAssembly.Module.

Syntax

Important: Since instantiation for large modules can be expensive, developers should only use the Instance() constructor when synchronous instantiation is absolutely required; the asynchronous WebAssembly.instantiateStreaming() method should be used at all other times.

new WebAssembly.Instance(module, importObject);

Parameters

module
The WebAssembly.Module object to be instantiated.
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 module or else a WebAssembly.LinkError is thrown.

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();
})

However, the preferred way to get an Instance is through the asynchronous WebAssembly.instantiateStreaming() function, for example 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());

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Instance() constructor 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
Instance() constructor 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Server
Node.js
Instance() constructor 8.0.0

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance/Instance