Run The Code From npm

Alright let's make a new small directory to test that we can now run this code and pull it from npm.

$ mkdir test
$ cd test

Now we need to create a package.json file that looks like this:

  "scripts": {
    "serve": "webpack-dev-server"
  "dependencies": {
    "@MYSCOPE/wasm-add": "^0.1.0"
  "devDependencies": {
    "webpack": "^4.0.1",
    "webpack-cli": "^2.0.10",
    "webpack-dev-server": "^3.1.0"

where MYSCOPE is your npm username. You can expand this to be a more complete file but we're really just trying to verify that this works!

Next up we'll need to create a small webpack configuration so that we can use the webpack-dev-server to serve the wasm file properly. It should be noted that webpack isn't a requirement. It's just what was chosen for this tutorial. You just need something to server the code! Here's what your webpack.config.js should look like:

const path = require('path');
module.exports = {
  entry: "./index.js",
  output: {
    path: path.resolve(__dirname, "dist"),
    filename: "index.js",
  mode: "development"

This tells webpack that if it's going to start things up use index.js. Before we do that though we'll need to setup a small html file. Create a new file called index.html and put this inside it:

<!DOCTYPE html>
    <meta charset="utf-8">
    <title>wasm-pack example</title>
    <script src="./index.js"></script>

We're almost set. Now we need to setup our JS file so that we can run some wasm code! Make a file called index.js and put this inside of it:

const js = import("@MYSCOPE/wasm-add/wasm_add.js");
js.then(js => {

Since web pack can't load wasm synchronously yet we are using the import statement above followed by the promise in order to load it properly. This is what lets us then call alert_add. We're importing from the node_module folder we haven't gotten yet so let's import all of our dependencies finally and run the example!

$ npm install
$ npm run serve

Then in a web browser navigate to http://localhost:8080 you should see something like this:

An alert box saying "Hello from Rust! 3 + 2 = 5"

If you did congrats you've successfully uploaded your first bit of wasm code to npm and used it properly!