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Using service workers, you can send push notifications to Chrome straight from your Node.js app. The excellent web-push npm module lets you send push notifications without going through an intermediary service like PubNub. This article will walk you through setting up a "Hello, World" example of web push notifications using a vanilla JavaScript frontend and Express on the backend. The final result will look like what you see below. The full source for this project is available on GitHub.

Credentials and Server Setup

In order to set up web push, you need to create a set of VAPID keys. VAPID keys identify who is sending the push notification. The web-push npm module can generate VAPID keys for you, so let's install web-push along with some other dependencies and use web-push generate-vapid-keys to create the keys.

$ npm install express@4.16.3 web-push@3.3.0 body-parser@1.18.2 express-static@1.2.5

+ express@4.16.3
+ web-push@3.3.0
+ body-parser@1.18.2
+ express-static@1.2.5
added 62 packages in 1.42s
$
$ ./node_modules/.bin/web-push generate-vapid-keys

=======================================

Public Key:
BOynOrGhgkj8Bfk4hsFENAQYbnqqLSigUUkCNaBsAmNuH6U9EWywR1JIdxBVQOPDbIuTaj0tVAQbczNLkC5zftw

Private Key:
<OMITTED>

=======================================

$

In order to support older browsers you may need to also get a GCM API key, but you don't need this in desktop Chrome 63 or higher.

Next, create a file called index.js that will contain your server. You'll need to require() and configure the web-push module with your VAPID keys. In the interest of simplicity, put the VAPID keys in the PUBLIC_VAPID_KEY and PRIVATE_VAPID_KEY environment variables.

const webpush = require('web-push');

const publicVapidKey = process.env.PUBLIC_VAPID_KEY;
const privateVapidKey = process.env.PRIVATE_VAPID_KEY;

// Replace with your email
webpush.setVapidDetails('mailto:val@karpov.io', publicVapidKey, privateVapidKey);

Next, add a /subscribe endpoint to your Express app. Your browser JavaScript will send an HTTP request to this endpoint with a PushSubscription object in the request body. You need the PushSubscription object in order to send a push notification via webpush.sendNotification().

const app = express();

app.use(require('body-parser').json());

app.post('/subscribe', (req, res) => {
  const subscription = req.body;
  res.status(201).json({});
  const payload = JSON.stringify({ title: 'test' });

  console.log(subscription);

  webpush.sendNotification(subscription, payload).catch(error => {
    console.error(error.stack);
  });
});

That's all you need on the server side. You can find the complete source on GitHub. Now, you need to create a client client.js and a service worker worker.js.

Client and Service Worker

First, in order to serve up your static assets to the client, use the express-static npm module to configure your Express app to serve static files from the top-level directory. Just make sure you put this app.use() call after your /subscribe route handler, otherwise Express will look for a subscribe.html file instead of using your route handler.

app.use(require('express-static')('./'));

Next, create an index.html file that will serve as an entry point for your application. The only part of this file that really matters is the <script> tag that pulls in the client-side JavaScript, the rest is a placeholder.

<html>
  <head>
    <title>Push Demo</title>
    <script type="application/javascript" src="/client.js"></script>
  </head>

  <body>
    Service Worker Demo
  </body>
</html>

Now that you have an entry point, create a JavaScript file called client.js. This file will be responsible for telling the browser to initialize your service worker and making the HTTP request to /subscribe. The below example uses async/await, because if your browser supports service workers it should support async/await as well.

// Hard-coded, replace with your public key
const publicVapidKey = 'BOynOrGhgkj8Bfk4hsFENAQYbnqqLSigUUkCNaBsAmNuH6U9EWywR1JIdxBVQOPDbIuTaj0tVAQbczNLkC5zftw';

if ('serviceWorker' in navigator) {
  console.log('Registering service worker');

  run().catch(error => console.error(error));
}

async function run() {
  console.log('Registering service worker');
  const registration = await navigator.serviceWorker.
    register('/worker.js', {scope: '/'});
  console.log('Registered service worker');

  console.log('Registering push');
  const subscription = await registration.pushManager.
    subscribe({
      userVisibleOnly: true,
      // The `urlBase64ToUint8Array()` function is the same as in
      // https://www.npmjs.com/package/web-push#using-vapid-key-for-applicationserverkey
      applicationServerKey: urlBase64ToUint8Array(publicVapidKey)
    });
  console.log('Registered push');

  console.log('Sending push');
  await fetch('/subscribe', {
    method: 'POST',
    body: JSON.stringify(subscription),
    headers: {
      'content-type': 'application/json'
    }
  });
  console.log('Sent push');
}

Finally, you need to implement the worker.js file that client.js loads. This is where your service worker logic lives. In a service worker, you get a 'push' event when your subscription receives a push notification.

console.log('Loaded service worker!');

self.addEventListener('push', ev => {
  const data = ev.data.json();
  console.log('Got push', data);
  self.registration.showNotification(data.title, {
    body: 'Hello, World!',
    icon: 'http://mongoosejs.com/docs/images/mongoose5_62x30_transparent.png'
  });
});

And that's it! Start your server with the correct environment variables:

$ env PUBLIC_VAPID_KEY='OMITTED' env PRIVATE_VAPID_KEY='OMITTED' node .

Navigate to http://localhost:3000 in Chrome, and you should see the below push notification!

These notifications aren't just limited to Chrome, this same code works with Firefox as well.

Moving On

Web push is just one of numerous advantages service workers provide. With a single npm module, you can send push notifications to most modern browsers. Give service workers a shot next time you want to add push notifications to your web app!