WebAssembly

BaselineWidely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since October 2017.

* Some parts of this feature may have varying levels of support.

TheWebAssembly JavaScript object acts as the namespace for allWebAssembly-related functionality.

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

Description

The primary uses for theWebAssembly object are:

Loading WebAssembly code, using theWebAssembly.instantiate() function.
Creating new memory and table instances via theWebAssembly.Memory()/WebAssembly.Table() constructors.
Providing facilities to handle errors that occur in WebAssembly via theWebAssembly.CompileError()/WebAssembly.LinkError()/WebAssembly.RuntimeError() constructors.

Interfaces

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 moreWebAssembly.Module instances. This allows dynamic linking of multiple modules.
WebAssembly.Instance: Is a stateful, executable instance of aWebAssembly.Module
WebAssembly.LinkError: Indicates an error during module instantiation (besidestraps from the start function).
WebAssembly.Memory: An object whosebuffer property is a resizableArrayBuffer that holds the raw bytes of memory accessed by a WebAssemblyInstance.
WebAssembly.Module: Contains stateless WebAssembly code that has already been compiled by the browser and can be efficientlyshared with Workers, and instantiated multiple times.
WebAssembly.RuntimeError: Error type that is thrown whenever WebAssembly specifies atrap.
WebAssembly.Table: An array-like structure representing a WebAssembly Table, which storesreferences, such as function references.
WebAssembly.Tag: An object that represents a type of WebAssembly exception.
WebAssembly.Exception: A WebAssembly exception object that can be thrown, caught, and rethrown both within and across WebAssembly/JavaScript boundaries.

Static methods

WebAssembly.compile(): Compiles aWebAssembly.Module from WebAssembly binary code, leaving instantiation as a separate step.
WebAssembly.compileStreaming(): Compiles aWebAssembly.Module directly from a streamed underlying source, leaving instantiation as a separate step.
WebAssembly.instantiate(): The primary API for compiling and instantiating WebAssembly code, returning both aModule and its firstInstance.
WebAssembly.instantiateStreaming(): Compiles and instantiates a WebAssembly module directly from a streamed underlying source, returning both aModule and its firstInstance.
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 ourinstantiate-streaming.html demo on GitHub, andview it live also) directly streams a Wasm module from an underlying source then compiles and instantiates it, the promise fulfilling with aResultObject. Because theinstantiateStreaming() function accepts a promise for aResponse object, you can directly pass it afetch() call, and it will pass the response into the function when it fulfills.

const importObject = {  my_namespace: { imported_func: (arg) => console.log(arg) },};WebAssembly.instantiateStreaming(fetch("simple.wasm"), importObject).then(  (obj) => obj.instance.exports.exported_func(),);

TheResultObject's.instance property is then accessed, and the contained exported function invoked.