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:

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

Methods

WebAssembly.instantiate()

The primary API for compiling and instantiating WebAssembly code, 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.validate()

Validates a given typed array of WebAssembly binary code, returning whether the bytes are valid WebAssembly code (true) or not (false).

Constructors

WebAssembly.Module()

Creates a new WebAssembly Module object.

WebAssembly.Instance()

Creates a new WebAssembly Instance object.

WebAssembly.Memory()

Creates a new WebAssembly Memory object.

WebAssembly.Table()

Creates a new WebAssembly Table object.

WebAssembly.CompileError()

Creates a new WebAssembly CompileError object.

WebAssembly.LinkError()

Creates a new WebAssembly LinkError object.

WebAssembly.RuntimeError()

Creates a new WebAssembly RuntimeError object.

Examples

After fetching some WebAssembly bytecode using fetch, we compile and instantiate the module using the WebAssembly.instantiate() function, importing a JavaScript function into the WebAssembly Module in the process. This promise resolves to an object (result) containing the compiled Module and Instance objects. We then call an Exported WebAssembly function that is exported by the Instance.

var importObject = {
  imports: {
    imported_func: function(arg) {
      console.log(arg);
    }
  }
};
fetch('simple.wasm').then(response =>
  response.arrayBuffer()
).then(bytes =>
  WebAssembly.instantiate(bytes, importObject)
).then(result =>
  result.instance.exports.exported_func()
);

Specifications

Browser compatibility

[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.

See also

• WebAssembly overview page
• WebAssembly concepts
• Using the WebAssembly JavaScript API