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The WebAssembly.compile() function compiles a WebAssembly.Module from WebAssembly binary code.  This function is useful if it is necessary to a compile a module before it can be instantiated (otherwise, the WebAssembly.instantiate() function should be used).


Promise<WebAssembly.Module> WebAssembly.compile(bufferSource);


A typed array or ArrayBuffer containing the binary code of the .wasm module you want to compile.

Return value

A Promise that resolves to a WebAssembly.Module object representing the compiled module.



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 compile() function and then sends it to a worker using postMessage().

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

fetch('simple.wasm').then(response =>
).then(bytes =>
).then(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, invoke an exported function from inside it, then show how we can return information on the available exports on a module using the WebAssembly.Module.exports property.

var importObject = {
  imports: {
    imported_func: function(arg) {

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

  WebAssembly.instantiate(mod, importObject).then(function(instance) {

  var exports = WebAssembly.Module.exports(mod);


Specification Status Comment
WebAssembly JavaScript API
The definition of 'compile()' in that specification.
Draft Initial draft definition.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support5716522 No4411
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support5757 Yes1522 No ?11

1. This feature is behind the Experimental JavaScript Features preference.

2. Disabled in the Firefox 52 Extended Support Release (ESR).

See also

Document Tags and Contributors

 Contributors to this page: chrisdavidmills, fscholz, lukewagner
 Last updated by: chrisdavidmills,