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.

WebAssembly.Module is a subclass of the hidden AbstractModuleSource class, in environments that support AbstractModuleSource.

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.

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.

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();
  });
};

Obtaining the module using import source

In environments that support source phase imports, you can obtain a WebAssembly.Module object using the import source statement or the import.source() operator. Both avoid the need to call fetch() or WebAssembly.compileStreaming(), relying instead on the default module loader machinery.

import source modSource from "./simple.wasm";

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

Specifications

Browser compatibility

See also

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