WebAssembly.Module

Baseline Widely 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.

A WebAssembly.Module object contains stateless WebAssembly code that has already been compiled by the browser — this can be efficiently shared with Workers, and instantiated multiple times.

Note: The WebAssembly.Module object is unrelated to the Module object used in Emscripten.

Constructor

WebAssembly.Module()

Creates a new Module object.

Static methods

WebAssembly.Module.customSections()

Given a Module and string, returns a copy of the contents of all custom sections in the module with the given string name.

WebAssembly.Module.exports()

Given a Module, returns an array containing descriptions of all the declared exports.

WebAssembly.Module.imports()

Given a Module, returns an array containing descriptions of all the declared imports.

Examples

Sending a compiled module to a worker

The following example compiles the loaded simple.wasm byte code using the WebAssembly.compileStreaming() method and sends the resulting Module instance to a worker using postMessage().

See the index-compile.html source code or view it live.

js
const worker = new Worker("wasm_worker.js");

WebAssembly.compileStreaming(fetch("simple.wasm")).then((mod) =>
  worker.postMessage(mod),
);

The worker function wasm_worker.js defines an import object for the module to use. The function then sets up an event handler to receive the module from the main thread. When the module is received, we create an instance from it using the WebAssembly.instantiate() method and invoke an exported function from inside it.

js
const importObject = {
  my_namespace: {
    imported_func(arg) {
      console.log(arg);
    },
  },
};

onmessage = (e) => {
  console.log("module received from main thread");
  const mod = e.data;

  WebAssembly.instantiate(mod, importObject).then((instance) => {
    instance.exports.exported_func();
  });
};

Specifications

Specification
WebAssembly JavaScript Interface
# modules

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
Module
Module() constructor
compileOptions parameter
customSections() static method
exports() static method
imports() static method

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
No support
No support

See also