Nishu Murmu | _Gliches

What Changed in Manifest V3?

Manifest V3 is the latest version of the Chrome Extensions platform. It introduces significant changes focused on security, privacy, and performance.

Key Differences

Background Scripts → Service Workers

The biggest change: persistent background pages are gone. They’re replaced by service workers which are event-driven and terminate when idle.

// manifest.json (V3)
{
  "manifest_version": 3,
  "background": {
    "service_worker": "background.js",
    "type": "module"
  }
}

Content Security Policy

Inline scripts are no longer allowed. You must use external script files:

{
  "content_security_policy": {
    "extension_pages": "script-src 'self'; object-src 'self'"
  }
}

declarativeNetRequest

The webRequest API is replaced by declarativeNetRequest for most use cases:

// Block ads declaratively
chrome.declarativeNetRequest.updateDynamicRules({
  removeRuleIds: [1],
  addRules: [{
    id: 1,
    priority: 1,
    action: { type: "block" },
    condition: {
      urlFilter: "||ads.example.com",
      resourceTypes: ["script", "image"]
    }
  }]
});

Migrating Your Extension

Update manifest_version to 3
Convert background scripts to service workers
Replace webRequest with declarativeNetRequest
Move inline scripts to external files
Update permission declarations

My Experience Migrating WhatsApp-Toggle

When I migrated my WhatsApp-Toggle extension, the main challenge was handling state in the service worker since it can terminate at any time.

// Use chrome.storage for persistent state
chrome.storage.local.get(["enabled"], (result) => {
  if (result.enabled) {
    activateToggle();
  }
});

Tips

Use chrome.storage for anything that needs to persist
Keep your service worker lean — it should wake up, do work, and sleep
Test with DevTools > Application > Service Workers
Use chrome.runtime.sendMessage for component communication

Resources

The transition to MV3 is mandatory now. Start migrating early to avoid last-minute issues.