Angular PWAs Interview Questions

This post lists some subjective questions and answers related to Progressive Web Apps (PWAs) in Angular. This collection contains some potential interview questions that may be helpful if you are preparing for a Frontend Engineering job interview specific to Angular framework. Check out Angular Interview Series – Topic Wise Q&A.

1. What is a PWA?

A Progressive Web App (PWA) is a type of application software delivered through the web, built using common web technologies including HTML, CSS, and JavaScript. PWAs offer a native app-like experience to users, allowing for offline capabilities, push notifications, and home screen installation. They are designed to work on any platform that uses a standard-compliant browser.

2. How to create a PWA in Angular?

To create a PWA in Angular, we need to add the PWA package to an existing angular application.

ng add @angular/pwa

This command automatically adds a service worker, a manifest file, and updates our Angular configuration.

Manifest file: The manifest.webmanifest file contains metadata about your app (e.g., name, icons, start URL). We can customize it according to our app’s requirements.

Service worker: The service worker is located in src/ngsw-config.json. We can define how caching should be managed for different assets.

3. What are the key features of PWAs?

• Responsive: PWAs work on any device and screen size.
• Offline Capability: They use service workers to cache resources and allow functionality even without an internet connection.
• Installable: Users can add PWAs to their home screens, providing a native app experience.
• Linkable: PWAs can be shared via URL without the need for installation from an app store.
• Push Notifications: They can send notifications to users, enhancing engagement.

4. What is a Service Worker and how does it work?

A Service Worker is a script that runs in the background of a web application, separate from the main browser thread. It enables features like caching, background sync, and push notifications.

How it works:

• Installation: When a PWA is loaded for the first time, the service worker gets registered and installed.
• Activation: After installation, it waits for all pages that use it to be closed before activating.
• Fetch Interception: Once active, it can intercept network requests, allowing it to serve cached resources or fetch from the network as needed.

5. How to implement caching strategies in Angular PWAs?

In ngsw-config.json, you can define different caching strategies. Key properties include:

• AssetGroups: Defines how static assets should be cached (e.g., images, CSS, JS).
• DataGroups: Specifies how to handle API calls and dynamic content.

Example:

{
  "index": "/index.html",
  "assetGroups": [
    {
      "name": "app",
      "installMode": "prefetch",
      "resources": {
        "files": [
          "/favicon.ico",
          "/index.html",
          "/*.css",
          "/*.js"
        ]
      }
    }
  ],
  "dataGroups": [
    {
      "name": "api",
      "urlPattern": "https://api.example.com/.*",
      "cacheConfig": {
        "maxSize": 100,
        "maxAge": "1h",
        "timeout": "10s",
        "strategy": "freshness"
      }
    }
  ]
}

In this example, the app will cache all CSS and JS files, and for API calls, it will cache responses for an hour.

6. How can you ensure a PWA is SEO-friendly?

PWAs can be made SEO-friendly by following these guidelines:

1. Server-Side Rendering (SSR): Use Angular Universal to pre-render pages on the server, ensuring search engines can crawl your content.
2. Meta Tags: Include relevant meta tags in your HTML for better indexing by search engines.
3. Proper URL Structure: Use clean, descriptive URLs.
4. Service Worker Strategies: Ensure your service worker doesn’t block critical resources from being crawled by search engines.
5. Manifest and Icons: Use a manifest file and icons that help browsers understand your app’s structure.

7. What are the limitations of PWAs?

While PWAs have many advantages, there are some limitations:

• Browser Support: Not all features are supported by every browser. Safari, for example, has limited PWA support compared to Chrome.
• Limited Device Features: Access to native device features (like Bluetooth, NFC, etc.) is limited compared to native apps.
• Performance: PWAs may not perform as well as native apps in certain scenarios, especially for heavy graphics or complex interactions.
• App Store Distribution: PWAs are not distributed through app stores, which might limit visibility compared to native apps.

8. How do you test a PWA?

Testing a PWA can be done using various tools and techniques:

1. Lighthouse: Use the Lighthouse tool available in Chrome DevTools to audit your PWA for performance, accessibility, SEO, and PWA-specific criteria.
2. Browser DevTools: Inspect service worker registration, cache storage, and network requests using the Application tab in Chrome DevTools.
3. Manual Testing: Test your PWA on various devices and browsers to ensure it functions as expected.
4. Automated Testing: Consider using tools like Protractor or Cypress for end-to-end testing.

9. How to handle push notifications in Angular PWAs?

To implement push notifications:

1. Request Permission: Ask users for permission to send notifications.

Notification.requestPermission().then(permission => {
  if (permission === 'granted') {
    console.log('Notification permission granted.');
  }
});

2. Service Worker Setup: Ensure your service worker can handle push events

self.addEventListener('push', event => {
  const options = {
    body: event.data ? event.data.text() : 'No payload',
    icon: 'icon.png',
    badge: 'badge.png'
  };
  event.waitUntil(
    self.registration.showNotification('Push Notification', options)
  );
});

3. Send Push Notifications: Use a backend service (like Firebase Cloud Messaging) to send push notifications to subscribed clients.

10. What are the best practices for developing Angular PWAs?

• Optimize Performance: Use lazy loading and optimize asset sizes to enhance loading speed.
• Use HTTPS: Serve your PWA over HTTPS to ensure security and trust.
• Test for Offline Capabilities: Make sure the PWA works offline and check its behavior in low-network conditions.
• Regularly Update Service Workers: Implement strategies for updating service workers to ensure users receive the latest version of your PWA.
• Monitor Analytics: Use tools like Google Analytics to track user engagement and performance metrics.

Building a PWA with Angular involves understanding both the Angular framework and the principles of PWAs. By following best practices and utilizing the right tools, we can create a robust application that enhances user experience while providing the benefits of modern web technology. For further clarification on any topic, feel free to explore the Angular Service Worker & PWAs Official Documentation.