WebAssembly.Module

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()

Creates a new Module object.

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.

The following example (see our index-compile.html demo on GitHub, and view it live also) compiles the loaded simple.wasm byte code using the WebAssembly.compileStreaming() method and then sends the resulting Module instance to a worker using postMessage().

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

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

In the worker (see wasm_worker.js) we define an import object for the module to use, then set 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.

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

onmessage = function(e) {
  console.log('module received from main thread');
  var mod = e.data;

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

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