WASM webpack loader
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- wasm-loader@1.3.0
Latest commit d4dbd36 Feb 20, 2018


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WASM Binary Module loader for Webpack

A simple .wasm binary file loader for Webpack. Import your wasm modules directly into your bundle as Constructors which return WebAssembly.Instance. This avoids the need to use fetch and parse for your wasm files. Imported wasm files are converted to Uint8Arrays and become part of the full JS bundle!


Install package: npm install --save wasm-loader


Edit webpack.config.js:

  loaders: [
      test: /\.wasm$/,
      loaders: ['wasm-loader']


Dead code elemination

This is an experimental feature and thus not activated by default.

You can activate it by passing dce=1 to the import and by specifying manually (for now) the exported elements you use, like the following example:

import createInstance from "./add.wasm?dce=1&add&test"

.then(m => {
  console.log(m.instance.exports.add(1, 2));

Everything else in the add.wasm binary will be removed.

Include wasm from your code

Grab your pre-built wasm file. For demo purposes we will use the excellent WasmExplorer. factorial.wasm file exports a function returning a factorial for a given number.

With the loader you can import this file directy

import makeFactorial from 'wasm/factorial';

The default export from the loader is a function returning native Promise. The promise resolves to a WebAssembly.Instance.

makeFactorial().then(instance => {
  // What is with the weird exports._Z4facti function?
  // This is how the function name is encoded by the C++ to wasm compiler
  const factorial = instance.exports._Z4facti;

  console.log(factorial(1)); // 1
  console.log(factorial(2)); // 2
  console.log(factorial(3)); // 6

deps can be passed in to override defaults. For example

  'global': {},
  'env': {
    'memory': new WebAssembly.Memory({initial: 100, limit: 1000}),
    'table': new WebAssembly.Table({initial: 0, element: 'anyfunc'})
}).then(instance => { /* code here */ });

Default deps are:

  'global': {},
  'env': {
    'memory': new Memory({initial: 10, limit: 100}),
    'table': new Table({initial: 0, element: 'anyfunc'})

A note about default deps(importsObject)

Default importsObject is meant to be used for a very basic wasm module. Most likely it will not suffice for something not dead simple compiled with emscripten. This is intentional. Supply your own imports to match the requirements of your wasm module(s). Some options are compiling your source code into S-syntax(.wast) examining that output, checking the imports. Compile the s-syntax file with asm2wasm into the final wasm module.