JavaScript Course

Progressive Web App (PWA) Enhancements

Install Service Worker

Service workers are the key to enabling offline functionality in your Progressive Web App (PWA). They are essentially event-driven scripts that run separately from the main browser thread, allowing you to intercept and handle network requests, cache resources, and more.

To install a service worker, you first need to create a service worker file. This file must be named serviceWorker.js and must be placed in the root of your web application. Here's a simple example of a service worker file:

self.addEventListener('install', (event) => {
  // Skip over the "wait until" for this example.
  event.waitUntil(
    caches.open('my-site-cache').then((cache) => {
      return cache.addAll([
        '/',
        '/index.html',
        '/styles.css',
        '/scripts.js',
      ]);
    })
  );
});

self.addEventListener('fetch', (event) => { event.respondWith( caches.match(event.request).then((response) => { return response || fetch(event.request); }) ); });

Once you have created your service worker file, you need to register it with your web application. You can do this by adding the following code to your index.html file:

<script>
  if ('serviceWorker' in navigator) {
    navigator.serviceWorker.register('/serviceWorker.js').then(() => {
      console.log('Service worker registered!');
    });
  }
</script>

Once your service worker is registered, it will start running in the background. It will intercept all network requests and handle them according to the logic you have defined in your service worker file.

Next Up: Cache Resources

Cache Resources

Now that you have installed a service worker, you can start caching resources. This will allow your PWA to load faster and work offline.

To cache a resource, you can use the Cache.addAll() method. This method takes an array of URLs as input and caches the corresponding resources.

For example, the following code caches the home page, index.html, the stylesheet styles.css, and the JavaScript file scripts.js:

caches.open('my-site-cache').then((cache) => {
  return cache.addAll([
    '/',
    '/index.html',
    '/styles.css',
    '/scripts.js',
  ]);
});

Once you have cached a resource, the service worker will intercept any subsequent requests for that resource and serve it from the cache. This will improve the performance of your PWA and make it more reliable.

Tips for Caching Resources

  • Cache static resources, such as HTML, CSS, and JavaScript files.
  • Don't cache resources that change frequently, such as data from a database.
  • Use a versioning system to invalidate old caches when you update your PWA.
  • Consider using a CDN (Content Delivery Network) to improve the performance of your cached resources.

Upcoming: Handle Network Requests

Handle network requests

Now that you have cached resources, you need to learn how to handle network requests. This will allow your PWA to work offline and provide a better user experience.

There are two main ways to handle network requests in a service worker:

  1. Intercept and respond to requests
  2. Intercept and modify requests

Intercept and respond to requests

The fetch event is fired when a network request is made. You can listen for this event and respond to it by returning a cached resource or a network response.

self.addEventListener('fetch', (event) => {
  event.respondWith(
    caches.match(event.request).then((response) => {
      return response || fetch(event.request);
    })
  );
});

This code snippet checks if the requested resource is cached. If it is, the cached resource is returned. Otherwise, the network request is made and the response is returned.

Intercept and modify requests

The request event is fired before a network request is made. You can listen for this event and modify the request before it is sent.

self.addEventListener('request', (event) => {
  // Modify the request object here

event.respondWith(fetch(event.request)); });

This code snippet allows you to modify the request object before it is sent. For example, you could add a header to the request or change the URL.

Next Up: Manage Push Notifications

Manage Push Notifications

Overview

Push notifications are a powerful way to engage with your users and keep them coming back to your PWA. They allow you to send messages to your users even when they are not actively using your app.

Implementation

Implementing push notifications in a PWA is a relatively simple process. First, you need to create a service worker file. This file will be responsible for handling the push notifications.

Once you have created your service worker file, you need to register it with your PWA. You can do this by adding the following code to your index.html file:

<script>
  if ('serviceWorker' in navigator) {
    navigator.serviceWorker.register('/serviceWorker.js');
  }
</script>

Once your service worker is registered, you can start sending push notifications. To do this, you will need to use the PushManager API.

The PushManager API provides a number of methods for sending push notifications. The most important method is the showNotification() method. This method takes a title and a body as arguments and displays a push notification to the user.

Here is an example of how to use the showNotification() method:

self.addEventListener('push', (event) =&gt; {
  const data = event.data.json();

self.registration.showNotification(data.title, { body: data.body, icon: '/icon.png', }); });

This code snippet listens for the push event. When a push event is received, the code snippet extracts the data from the event and then uses the showNotification() method to display a push notification to the user.

Tips for Managing Push Notifications

Here are a few tips for managing push notifications:

  • Use a clear and concise title and body. The title and body of your push notifications should be clear and concise so that users can quickly understand what the notification is about.
  • Send push notifications at a regular time. Users are more likely to open push notifications if they are sent at a regular time.
  • Don't send too many push notifications. If you send too many push notifications, users may become annoyed and unsubscribe from your notifications.
  • Use push notifications to promote your content. Push notifications are a great way to promote your content and drive traffic to your website.

Next Up: Show a Splash Screen After Installation

Show a Splash Screen After Installation

When a user installs your PWA from the app store, you can show them a splash screen while the app is loading. This will provide a more polished and professional experience for your users.

To show a splash screen, you will need to use the oninstall event. This event is fired when the PWA is installed.

In your service worker file, add the following code:

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open('splash-screen').then((cache) => {
      return cache.addAll([
        '/splash-screen.png',
        '/splash-screen.css',
        '/splash-screen.js',
      ]);
    })
  );
});

This code will cache the files needed for your splash screen.

Next, you need to add a fetch event listener to your service worker file. This event listener will intercept all network requests and serve the cached splash screen files if the request matches the URL of one of the splash screen files.

self.addEventListener('fetch', (event) => {
  if (event.request.url.includes('/splash-screen')) {
    event.respondWith(
      caches.match(event.request).then((response) => {
        return response || fetch(event.request);
      })
    );
  }
});

Finally, you need to add the following code to your index.html file:

<link rel="preload" href="/splash-screen.css" as="style">
<link rel="preload" href="/splash-screen.js" as="script">

This code will preload the splash screen CSS and JS files so that they are available when the PWA is installed.

When a user installs your PWA, the splash screen will be displayed while the app is loading. Once the app is loaded, the splash screen will be removed.

This is just a basic example of how to show a splash screen after installation. You can customize the splash screen to match the look and feel of your PWA.

Next Up: Update and Remove Old Service Workers

Update and Remove Old Service Workers

Keeping your service workers up to date is essential for the smooth operation of your PWA. As you make changes to your app, you'll need to update your service worker to reflect those changes.

How to Update Service Workers

Updating your service worker is a simple process. Just create a new service worker file and register it with your app. The new service worker will automatically take over from the old one.

Here's an example of a new service worker file:

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open('my-site-cache-v2').then((cache) => {
      return cache.addAll([
        '/',
        '/index.html',
        '/styles.css',
        '/scripts.js',
      ]);
    })
  );
});

self.addEventListener('activate', (event) => { event.waitUntil( caches.keys().then((cacheNames) => { return Promise.all( cacheNames.map((cacheName) => { if (cacheName !== 'my-site-cache-v2') { return caches.delete(cacheName); } }) ); }) ); });

self.addEventListener('fetch', (event) => { event.respondWith( caches.match(event.request).then((response) => { return response || fetch(event.request); }) ); });

As you can see, the new service worker file is very similar to the old one. The only difference is that the cache name has been changed to my-site-cache-v2. This will tell the browser that this is a new version of the service worker.

When you register the new service worker, the browser will automatically activate it. The old service worker will be deactivated and its caches will be deleted.

How to Remove Old Service Workers

If you have multiple old service workers registered with your app, you may want to remove them to improve performance. To remove an old service worker, use the unregister() method:

navigator.serviceWorker.unregister('old-service-worker.js');

You should only remove old service workers that are no longer needed. If you remove a service worker that is still in use, your app may not work properly.

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