Service Workers — Complete Guide
Service Workers — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of JavaScript Tutorial on Toolliyo Academy.
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JavaScript Tutorial · Lesson 69 of 100
Service Workers
Basics ✓ → Objects & data ✓ → Async & DOM ✓ → Advanced → Tools → Projects
Advanced · 4 — Production skills · ~10 min · JS Advanced
What is this?
Service workers are background scripts that intercept network requests — enable offline apps and push notifications.
Why should you care?
PWAs cache assets and work with flaky networks.
See it live — copy this example
Paste into an HTML file or the browser console (F12). Use Run below when the live editor is available.
// Register from main page (HTTPS required)
// if ("serviceWorker" in navigator) {
// navigator.serviceWorker.register("/sw.js");
// }Run Example »
Edit the code below and click Run to see the result in Toolliyo’s live editor.
What happened?
- sw.js listens for fetch events and can return cached responses.
- Lifecycle: install → activate → fetch.
Practice next
- Sketch register("/sw.js") on load.
- Read install → activate → fetch lifecycle.
- Inspect Application → Service Workers tab.
- Comment network-first vs cache-first strategies for API vs static assets.
- Add skipWaiting message flow sketch for updates.
Remember
Background network proxy HTTPS only Powers offline PWAs
ScriptVerse field app PWA
Service worker caches shell assets so CRM works offline for sales reps with poor connectivity.
Outcome: PWAs extend ScriptVerse reach to unreliable networks with installable web apps.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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