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WebAssembly

The WebAssembly JavaScript object acts as the namespace for all WebAssembly-related functionality.

Unlike most other global objects, WebAssembly is not a constructor (it is not a function object). You can compare it to Math, which is also a namespace object for mathematical constants and functions, or to Intl which is the namespace object for internationalization constructors and other language-sensitive functions.

Description

The primary uses for the WebAssembly object are:

Constructor properties

WebAssembly.CompileError()
Indicates an error during WebAssembly decoding or validation.
WebAssembly.Global()
Represents a global variable instance, accessible from both JavaScript and importable/exportable across one or more WebAssembly.Module instances. This allows dynamic linking of multiple modules.
WebAssembly.Instance()
Is a stateful, executable instance of a WebAssembly.Module
WebAssembly.LinkError()
Indicates an error during module instantiation (besides traps from the start function).
WebAssembly.Memory()
An object whose buffer property is a resizable ArrayBuffer that holds the raw bytes of memory accessed by a WebAssembly Instance.
WebAssembly.Module()
Contains stateless WebAssembly code that has already been compiled by the browser and can be efficiently shared with Workers, and instantiated multiple times.
WebAssembly.RuntimeError()
Error type that is thrown whenever WebAssembly specifies a trap.
WebAssembly.Table()
An array-like structure representing a WebAssembly Table, which stores function references.

Static methods

WebAssembly.instantiate()
The primary API for compiling and instantiating WebAssembly code, returning both a Module and its first Instance.
WebAssembly.instantiateStreaming()
Compiles and instantiates a WebAssembly module directly from a streamed underlying source, returning both a Module and its first Instance.
WebAssembly.compile()
Compiles a WebAssembly.Module from WebAssembly binary code, leaving instantiation as a separate step.
WebAssembly.compileStreaming()
compiles a WebAssembly.Module directly from a streamed underlying source, leaving instantiation as a separate step.
WebAssembly.validate()
Validates a given typed array of WebAssembly binary code, returning whether the bytes are valid WebAssembly code (true) or not (false).

Examples

Stream a .wasm module then compile and instantiate it

The following example (see our instantiate-streaming.html demo on GitHub, and view it live also) directly streams a .wasm module from an underlying source then compiles and instantiates it, the promise fulfilling with a ResultObject. Because the instantiateStreaming() function accepts a promise for a Response object, you can directly pass it a WindowOrWorkerGlobalScope.fetch() call, and it will pass the response into the function when it fulfills.

var importObject = { imports: { imported_func: arg => console.log(arg) } };

WebAssembly.instantiateStreaming(fetch('simple.wasm'), importObject)
.then(obj => obj.instance.exports.exported_func());

The ResultObject's instance member is then accessed, and the contained exported function invoked.

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
WebAssembly 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
CompileError 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
Global 69 No 62 No No 13.1
Instance 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
LinkError 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
Memory 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
Module 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
RuntimeError 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
Table 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
compile 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
compileStreaming 61 16 58 No 47 No
instantiate 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
instantiateStreaming 61 16 58 No 47 No
validate 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
WebAssembly 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
CompileError 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Global 69 69 62 No 13.4 10.0
Instance 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
LinkError 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Memory 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Module 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
RuntimeError 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Table 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
compile 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
compileStreaming 61 61 58 45 No 8.0
instantiate 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
instantiateStreaming 61 61 58 45 No 8.0
validate 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Server
Node.js
WebAssembly 8.0.0
CompileError 8.0.0
Global No
Instance 8.0.0
LinkError 8.0.0
Memory 8.0.0
Module 8.0.0
RuntimeError 8.0.0
Table 8.0.0
compile 8.0.0
compileStreaming No
instantiate 8.0.0
instantiateStreaming No
validate 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