WebAssembly

The WebAssembly JavaScript object represents the WebAssembly environment in JavaScript, and acts as the namespace for all WebAssembly-related functionality.

Syntax

WebAssembly

Description

The primary uses for the WebAssembly object are:

• Compiling/instantiating wasm modules that have been loaded into a JavaScript instance as typed arrays, using the WebAssembly.compile()/WebAssembly.instantiate() methods. You can also compile a new module using the WebAssembly.Module() constructor.
• Creating new memory and table instances via the WebAssembly.Memory()/WebAssembly.Table() constructors.
• Create new wasm instances from compiled modules via the WebAssembly.Instance() constructor.
• Providing facilities to handle errors that occur in WebAssembly via the WebAssembly.CompileError()/WebAssembly.LinkError()/WebAssembly.RuntimeError() constructors.

Constructors

WebAssembly.Module()

Creates a new WebAssembly Module object instance.

WebAssembly.Instance()

Creates a new WebAssembly Instance object instance.

WebAssembly.Memory()

Creates a new WebAssembly Memory object instance.

WebAssembly.Table()

Creates a new WebAssembly Table object instance.

WebAssembly.CompileError()

Creates a new WebAssembly CompileError object instance.

WebAssembly.LinkError()

Creates a new WebAssembly LinkError object instance.

WebAssembly.RuntimeError()

Creates a new WebAssembly RuntimeError object instance.

Methods

WebAssembly.compile()

Compiles a .wasm file loaded into the JavaScript context as a typed array (e.g. using Fetch/arrayBuffer into a Module object instance.

WebAssembly.instantiate()

Compiles a .wasm file loaded into the JavaScript context as a typed array (e.g. using Fetch/arrayBuffer into a Module object instance and then instantiates that module, all in one step — it returns an Instance object instance.

WebAssembly.validate()

Validates a given array buffer source, returning a Boolean that specifies whether the source is valid wasm code (true) or not (false).

Examples

The following example compiles and instantiates the loaded simple.wasm byte code using the WebAssembly.instantiate() method, importing a JavaScript function into the WebAssembly Module in the process — this promise resolves to an object (obj) containing the compiled Module instance, and it's instantiated Instance instance. We then export a function from the module via Instance.exports.exported_func().

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

fetch('simple.wasm').then(function(response) {
  response.arrayBuffer().then(function(bytes) {
    WebAssembly.instantiate(bytes, importObject).then(function(obj) {
      obj.instance.exports.exported_func();
    })
  })
});

Specifications

Specification	Status	Comment
Web Assembly JavaScript API The definition of 'WebAssembly' in that specification.	Draft	Initial draft definition.

Browser compatibility

[1] Experimental support can be enabled in Chrome 51+ and Opera 38+ by going to chrome://flags and enabling the Experimental WebAssembly flag.

[2] Experimental support can be enabled in Firefox 47+ by enabling the javascript.options.wasm flag in about:config.

See also

• WebAssembly landing page.
• WebAssembly concepts
• Using the WebAssembly JavaScript API