Lesson 30 / 30
PWA interview questions
Prepare for PWA interviews on service worker lifecycle, caching strategies, offline-first design and update handling.
Core PWA concepts
Common interview topics: What defines a PWA? Service worker lifecycle? Caching strategies? Difference between offline-first and network-first? How to handle service worker updates? What is the app shell model?
Sample Q&A
Interview answer examples for common PWA questions.
**Q: What's the difference between network-first and cache-first?**
A: Network-first fetches from the network first, falling back to cache if offline—ideal for pages that change often. Cache-first serves from cache immediately, checking the network for updates—ideal for static assets.
**Q: How do you handle service worker updates?**
A: Listen to the 'controllerchange' event and the 'message' event in the service worker. Use skipWaiting() to activate immediately or notify users to refresh.
**Q: What's the app shell model?**
A: The app shell is the minimal static shell (HTML, CSS, JS) cached aggressively. Dynamic content loads separately. This pattern enables instant loads and offline-first architecture.Output:
Common interview questions and comprehensive answers prepared.
Interview tips
Prepare with: Building a demo PWA, explaining trade-offs in caching strategies, discussing real-world PWA implementations (Twitter Lite, Spotify), and understanding browser compatibility.
Quick check
Quick check: What is the main purpose of a service worker in a PWA?
- Render the user interface
- Store user authentication tokens
- Compile TypeScript to JavaScript
- Intercept network requests, enable offline functionality, and handle caching
Answer
Intercept network requests, enable offline functionality, and handle caching — Service workers are background scripts that intercept requests, manage caches, and enable offline support.
Final quiz 1 of 8
Final quiz
Quick check: Which file tells browsers how to install and display a PWA?
- package.json
- robots.txt
- manifest.json
- sitemap.xml
Answer
manifest.json — The web app manifest holds name, icons, start_url and display mode.
Final quiz 2 of 8
Final quiz
Quick check: Where must a service worker be served from (except localhost)?
- Any HTTP page
- A file URL
- A USB drive
- HTTPS
Answer
HTTPS — Service workers require a secure context.
Final quiz 3 of 8
Final quiz
Quick check: Which strategy suits versioned static assets?
- Cache-first
- Network-only
- No caching
- Random
Answer
Cache-first — Fingerprinted assets rarely change, so serving from cache is fastest.
Final quiz 4 of 8
Final quiz
Quick check: What does event.waitUntil() do in install?
- Skips the event
- Keeps the event alive until a promise settles
- Stops the worker
- Clears the cache
Answer
Keeps the event alive until a promise settles — It ensures caching work finishes before the event ends.
Final quiz 5 of 8
Final quiz
Quick check: Which API stores large structured offline data?
- localStorage only
- Cookies
- IndexedDB
- window.name
Answer
IndexedDB — IndexedDB handles structured, larger datasets asynchronously.
Final quiz 6 of 8
Final quiz
Quick check: When should you ask for push permission?
- Immediately on page load
- Never
- On every click
- After the user shows interest, in context
Answer
After the user shows interest, in context — Contextual prompts get far higher acceptance.
Final quiz 7 of 8
Final quiz
Quick check: Which header setting helps users get a new service worker quickly?
- Cache-Control: no-cache on sw.js
- Cache-Control: max-age=31536000 on sw.js
- Expires: never
- Set-Cookie
Answer
Cache-Control: no-cache on sw.js — A cached sw.js can delay updates.
Final quiz 8 of 8
Final quiz
Quick check: What is feature detection for PWAs?
- Detecting viruses
- Checking an API exists before using it
- Compressing images
- Installing plugins
Answer
Checking an API exists before using it — e.g. 'serviceWorker' in navigator keeps older browsers working.