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 |
|---|---|---|
| WebAssembly JavaScript API The definition of 'Instance' in that specification. |
Draft | Initial draft definition. |
Browser compatibility
| Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
| Basic support | 57 | 16 | 522 | No | 44 | 11 |
exports | 57 | 16 | 522 | No | 44 | 11 |
prototype | 57 | 16 | 522 | No | 44 | 11 |
| Feature | Android webview | Chrome for Android | Edge mobile | Firefox for Android | IE mobile | Opera Android | iOS Safari |
|---|---|---|---|---|---|---|---|
| Basic support | 57 | 57 | Yes1 | 522 | No | ? | 11 |
exports | 57 | 57 | Yes1 | 522 | No | ? | 11 |
prototype | 57 | 57 | Yes1 | 522 | No | ? | 11 |
1. This feature is behind the Experimental JavaScript Features preference.
2. Disabled in the Firefox 52 Extended Support Release (ESR).