Fix Service Worker Registration Failed in Svelte

Service Worker Registration Failed in Svelte

Service worker registration failures prevent your Svelte app from working offline, receiving push notifications, or caching assets. The browser silently fails, leaving users with a degraded experience.

Common Failure Reasons

• Service worker file not found (wrong path or not built)
• HTTPS not enabled (required except on localhost)
• MIME type mismatch — server returns HTML instead of JavaScript
• Scope misconfiguration

How to Fix

// Bad: assuming registration always succeeds
navigator.serviceWorker.register("/sw.js");

// Good: proper error handling and debugging
if ("serviceWorker" in navigator) {
  navigator.serviceWorker
    .register("/sw.js", { scope: "/" })
    .then((reg) => {
      console.log("SW registered:", reg.scope);
    })
    .catch((err) => {
      console.error("SW registration failed:", err);
      // Common fixes:
      // 1. Verify /sw.js returns JS (not HTML 404 page)
      // 2. Check HTTPS is enabled
      // 3. Ensure sw.js is in the correct public directory
    });
}

Debugging Steps

1. Open DevTools > Application > Service Workers
2. Check the Network tab — is sw.js returning 200 with application/javascript?
3. Verify the file is in your Svelte static/public directory
4. Test on HTTPS or localhost only

Bugsly Monitors SW Health

[Bugsly](https://bugsly.io) captures service worker registration failures across your user base, showing you failure rates by browser, OS, and network condition — so you know if it's a build issue or an environment problem.