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Rust + WebAssembly + JavaScript


WebAssembly is the new craze when it comes to frontend & backend capabilities. The part that has me excited about it is the concept that you can use the same library for both frontend & backend. (provided the backend is in Rust or NodeJs.)

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Getting Started

Expected Prerequisites:

First, we need to establish the goal of this little tutorial. This tutorial is to give a little demonstration of how to simply get Webpack to compile our Rust code into WebAssembly and import it on the frontend. To get started, lets create a new folder and enter it:

mkdir -p ./wasm-demo
cd ./wasm-demo
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Now with this empty folder, lets start by adding the necessary files to get up and running.

Setting up Yarn

If you are curious why Yarn 2+, click here!

For the yarn init, you can simply select all the defaults.

yarn init 
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We are converting this project to a Yarn 2+ for speed.

yarn set version berry
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Getting our rust crate created

cargo new \
  --edition 2021 \
  --lib \
  --name hello-world \
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Adding the root Cargo.toml

Now, create a new file called Cargo.toml in the root of your project. The contents of the Cargo.toml should be a simple workspace:

members = [
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We create a Cargo.toml at the root of the project to allow us to have multiple crates in a given repository and manage them all together.

Finally, adding JavaScript dependencies

Development dependencies

yarn add -D \
  webpack \
  webpack-cli \
  webpack-dev-server \
  @wasm-tool/wasm-pack-plugin \
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Configuring Webpack

Getting the Webpack configurations to be just right can be tedious for any project. However, with Rust & WebAssembly it can be relatively easy! Lets start by creating the files we will need to get running:

Setting up the basic files

Our application directory:

mkdir -p ./src
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Webpack config file:

touch ./webpack.config.js
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Basic application file:

touch ./src/index.js
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Editing the webpack config

// Path lets us map out where files should be:
const path = require("path");

// HtmlWebpackPlugin will let us inject html into our app
const HtmlWebpackPlugin = require('html-webpack-plugin');

// WasmPackPlugin does the magic of building our application
const WasmPackPlugin = require('@wasm-tool/wasm-pack-plugin');

module.exports = {
    experiments: {
        // This allows WebAssembly to be bundled
        asyncWebAssembly: true
    // Its good practice to specify the mode
    // But this can also be done via `--mode`
    mode: process.env.NODE_ENV || "development",
    // This entry should be pathing to the index.js
    entry: path.join(__dirname, "src/index.js"),
    output: {
        // Always clean your output folder!
        // Otherwise, you can end up with dangling code when developing.
        clean: true,
        path: path.resolve(__dirname, './dist'),
        filename: 'bundle.js',
    plugins: [
        // We point our WasmPackPlugin to the location of the
        // the crates `Cargo.toml` file. Never the root file.
        new WasmPackPlugin({
            crateDirectory: path.join(__dirname, "hello-world")
        // Some basic boiler plate, 
        // Device width meta lets us make it mobile friendly. 
        new HtmlWebpackPlugin({
            meta: {viewport: 'width=device-width, initial-scale=1, shrink-to-fit=no'},
            // This will be used later
            templateContent: "<div id='app'></div>",
            inject: "body"
    resolve: {
        // A little overkill for our tutorial but useful.
        extensions: [".ts", ".tsx", ".js", ".jsx", '.mts', '.mjs', '...'],
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Getting our Rust code ready

Adding Dependencies

In order to compile to WebAssembly, we need to make a few adjustments. First, we will need to install the build tools:

cargo install wasm-pack
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Next, we will need to modify the hello-world/Cargo.toml file:

name = "hello-world"
version = "0.1.0"
edition = "2021"

# We add cdylib and rlib to tell rust
# it needs to build for WebAssembly and Rust
crate-type = ["cdylib", "rlib"]

# wasm-bindgen builds the JavaScript bindings
# Take a look at the following link for more info:
wasm-bindgen = "0"
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Adding a main function

Now, we edit the file at hello-world/src/

use wasm_bindgen::prelude::*;

// The main function which will be referenced in JavaScript
pub fn main() -> String {
    // Returning a string to use in JavaScript land.
    String::from("Hello, world!")
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Building to ensure it works

At the root of the project, run the following command to make sure the rust code is good:

cargo build
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You should get a success build:
Successful Build

Getting our JavaScript code ready

Now that we have our Rust code ready to rock and roll, lets get our JavaScript ready by editing the src/index.js file:

 * When importing a Rust WebAssembly crate,
 * you must always add a /pkg to the import like below.
 * This is because, when webpack builds the crate it will output the contents into a pkg folder.
 * If you wish to manually build, you can use the command `wasm-pack build --target web` inside the `hello-world` folder
import * as helloWorld from '../hello-world/pkg'

document.getElementById("app").innerText =
     * Now we can simply call the function `main` from our Rust package :)

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Running the code

Now we have all of our code set up and ready to go! If we simply run:

yarn webpack serve
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It should build the project successfully and give you a web address you can use to access your application! look for loopback and click that url or open it up in your browser:

Once the application is open in your browser, it should look a little something like this:

Successful App


Click here to take a look at the source!

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