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This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

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
Web Assembly JavaScript API
The definition of 'compile()' in that specification.
Draft Initial draft definition.

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 57 15[2] 52 (52)[1] No support 44 11
Feature Chrome for Android Android Webview Edge Mobile Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 57 57 No support 52.0 (52)[1] No support No support 11

[1] WebAssembly is enabled in Firefox 52+, although disabled in the Firefox 52 Extended Support Release (ESR.)

[2] Currently supported behind the “Experimental JavaScript Features” flag. See this blog post for more details.

See also

Document Tags and Contributors

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