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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.

The WebAssembly.Instance() constructor function can be called to synchronously instantiate a given WebAssembly.Module object. However, the primary way to get an Instance is through the asynchronous WebAssembly.instantiateStreaming() function.

Constructor 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.

var myInstance = 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.

`Instance` instances

All Instance instances inherit from the Instance() constructor's prototype object — this can be modified to affect all Instance instances.

Instance properties

Instance.prototype.constructor: Returns the function that created this object's instance. By default this is the WebAssembly.Instance() constructor.
Instance.prototype.exports Read only: 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.

Instance methods

None.

Specifications

Specification	Status	Comment
WebAssembly JavaScript Interface The definition of 'Instance' in that specification.	Working Draft	Initial draft definition.

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	57	16	52 52 Disabled in the Firefox 52 Extended Support Release (ESR).	No	44	11
`exports`	57	16	52 52 Disabled in the Firefox 52 Extended Support Release (ESR).	No	44	11
`prototype`	57	16	52 52 Disabled in the Firefox 52 Extended Support Release (ESR).	No	44	11

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	57	57	Yes Disabled Yes Disabled Disabled This feature is behind the `Experimental JavaScript Features` preference.	52 52 Disabled in the Firefox 52 Extended Support Release (ESR).	?	11	7.0
`exports`	57	57	Yes Disabled Yes Disabled Disabled This feature is behind the `Experimental JavaScript Features` preference.	52 52 Disabled in the Firefox 52 Extended Support Release (ESR).	?	11	7.0
`prototype`	57	57	Yes Disabled Yes Disabled Disabled This feature is behind the `Experimental JavaScript Features` preference.	52 52 Disabled in the Firefox 52 Extended Support Release (ESR).	?	11	7.0

	Server
	Node.js
Basic support	8.0.0
`exports`	8.0.0
`prototype`	8.0.0