WebAssembly.compile()

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.

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

Note: Webpages that have strict Content Security Policy (CSP) might block WebAssembly from compiling and executing modules. For more information on allowing WebAssembly compilation and execution, see the script-src CSP.

Syntax

js
WebAssembly.compile(bufferSource)
WebAssembly.compile(bufferSource, compileOptions)

Parameters

bufferSource

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

compileOptions Optional

An object containing compilation options. Properties can include:

builtins Optional

An array of one or more strings that enables the usage of JavaScript builtins in the compiled Wasm module. The strings define the builtins you want to enable. Currently the only available value is "js-string", which enables JavaScript string builtins.

importedStringConstants Optional

A string specifying a namespace for imported global string constants. This property needs to be specified if you wish to use imported global string constants in the Wasm module.

Return value

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

Exceptions

If bufferSource is not a typed array or ArrayBuffer, the promise rejects with a TypeError.
If compilation fails, the promise rejects with a WebAssembly.CompileError.

Examples

Using compile

The following example compiles the loaded simple.wasm byte code using the compile() function and then sends it to a worker using postMessage().

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

fetch("simple.wasm")
  .then((response) => response.arrayBuffer())
  .then((bytes) => WebAssembly.compile(bytes))
  .then((mod) => worker.postMessage(mod));

Note: You'll probably want to use WebAssembly.compileStreaming() in most cases, as it is more efficient than compile().

Enabling JavaScript builtins and global string imports

This example enables JavaScript string builtins and imported global string constants when compiling the Wasm module with compile(), before instantiating it with instantiate() then running the exported main() function (which logs "hello world!" to the console). See it running live.

js
const importObject = {
  // Regular import
  m: {
    log: console.log,
  },
};

const compileOptions = {
  builtins: ["js-string"], // Enable JavaScript string builtins
  importedStringConstants: "string_constants", // Enable imported global string constants
};

fetch("log-concat.wasm")
  .then((response) => response.arrayBuffer())
  .then((bytes) => WebAssembly.compile(bytes, compileOptions))
  .then((module) => WebAssembly.instantiate(module, importObject))
  .then((instance) => instance.exports.main());