WebAssembly.module

The Module() constructor of the WebAssembly global object creates a new Module object instance.

A Module object instance is a JavaScript wrapper around a wasm module. You can create one using the WebAssembly.Module() constructor, or the WebAssembly.compile() method.

Syntax

var myModule = new WebAssembly.Module(bufferSource);

Parameters

bufferSource

An ArrayBuffer containing the byte code for a WebAssembly module, e.g. loaded using XMLHttpRequest or the Fetch API.

Module Constructor Methods

WebAssembly.Module.customSections()

Returns an array containing references to the custom sections available in a given WebAssembly module.

WebAssembly.Module.exports()

Returns an array containing references to the exported functions available in a given WebAssembly module.

WebAssembly.Module.imports()

Returns an array containing references to the imported functions available in a given WebAssembly module.

Module instances

All Module instances inherit from the Module() constructor's prototype object — this can be modified to affect all Module instances.

Instance properties

Module.prototype.constructor

Returns the function that created this object's instance. By default this is the Number object.

Instance methods

Module instances have no default methods of their own.

Examples

The following example (see our index-compile.html test file on GitHub, and view it live also) compiles the loaded simple.wasm byte code using the WebAssembly.compile() method, and then creates an instance using the WebAssembly.Instance() constructor.

It then imports a JavaScript function into the WebAssembly Module in the process, and then exports a function from the module via Instance.exports.

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

fetch('simple.wasm').then(function(response) {
  response.arrayBuffer().then(function(bytes) {
    WebAssembly.compile(bytes).then(function(mod) {
      var instance = new WebAssembly.Instance(mod, importObject);
      instance.exports.exported_func();
    })
  })
});

The module instance in this case is the value returned when the compile() promise resolves (mod). You could also compile and instantiate using the relevant constructors, e.g.:

var testMod = new WebAssembly.Module(bytes);
var testInst = new WebAssembly.Instance(testMod, importObject);

Specifications

Specification	Status	Comment
Web Assembly JavaScript API The definition of 'WebAssembly.Module()' 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