This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.
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.instantiate() 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.instantiate() method should be used at all other times.
var myInstance = new WebAssembly.Instance(module, importObject);
Parameters
- module
- The
WebAssembly.Moduleobject to be instantiated. - importObject Optional
- An object containing the values to be imported into the newly-created
Instance, such as functions orWebAssembly.Memoryobjects. There must be one matching property for each declared import ofmoduleor 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.exportsRead 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 |
|---|---|---|
| Web Assembly JavaScript API The definition of 'Instance' in that specification. |
Draft | Initial draft definition. |
Browser compatibility
| Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
|---|---|---|---|---|---|---|
| Basic support | 57 | 15[2] | 52 (52)[1] | No support | 44 | 11 |
| Feature | Chrome for Android | Android Webview | Edge Mobile | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|---|
| Basic support | 57 | 57 | No support | 52.0 (52)[1] | No support | No support | 11 |
[1] WebAssembly is enabled in Firefox 52+, although disabled in the Firefox 52 Extended Support Release (ESR.)
[2] Currently supported behind the “Experimental JavaScript Features” flag. See this blog post for more details.