Hello, World!

View full source code or view the compiled example online

This is the "Hello, world!" example of #[wasm_bindgen] showing how to set up a project, export a function to JS, call it from JS, and then call the alert function in Rust.


The Cargo.toml lists the wasm-bindgen crate as a dependency.

Also of note is the crate-type = ["cdylib"] which is largely used for wasm final artifacts today.

name = "hello_world"
version = "0.1.0"
authors = ["The wasm-bindgen Developers"]
edition = "2018"

crate-type = ["cdylib"]

wasm-bindgen = "0.2.64"


Here we define our Rust entry point along with calling the alert function.

# #![allow(unused_variables)]
#fn main() {
use wasm_bindgen::prelude::*;

extern "C" {
    fn alert(s: &str);

pub fn greet(name: &str) {
    alert(&format!("Hello, {}!", name));



Our JS entry point is quite small!

// Note that a dynamic `import` statement here is required due to
// webpack/webpack#6615, but in theory `import { greet } from './pkg';`
// will work here one day as well!
const rust = import('./pkg');

  .then(m => m.greet('World!'))

Webpack-specific files

Note: Webpack is not required for this example, and if you're interested in options that don't use a JS bundler see other examples.

And finally here's the Webpack configuration and package.json for this project:


const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const webpack = require('webpack');
const WasmPackPlugin = require("@wasm-tool/wasm-pack-plugin");

module.exports = {
    entry: './index.js',
    output: {
        path: path.resolve(__dirname, 'dist'),
        filename: 'index.js',
    plugins: [
        new HtmlWebpackPlugin(),
        new WasmPackPlugin({
            crateDirectory: path.resolve(__dirname, ".")
        // Have this example work in Edge which doesn't ship `TextEncoder` or
        // `TextDecoder` at this time.
        new webpack.ProvidePlugin({
          TextDecoder: ['text-encoding', 'TextDecoder'],
          TextEncoder: ['text-encoding', 'TextEncoder']
    mode: 'development'


  "scripts": {
    "build": "webpack",
    "serve": "webpack-dev-server"
  "devDependencies": {
    "@wasm-tool/wasm-pack-plugin": "1.0.1",
    "text-encoding": "^0.7.0",
    "html-webpack-plugin": "^3.2.0",
    "webpack": "^4.29.4",
    "webpack-cli": "^3.1.1",
    "webpack-dev-server": "^3.1.0"