migration-guide

# Manifest V2 to V3 Migration Guide

## Overview of Changes

| Feature | Manifest V2 | Manifest V3 |
|---------|-------------|-------------|
| Background | Persistent page | Service worker |
| Remote code | Allowed | Forbidden |
| Web requests | webRequest API | declarativeNetRequest |
| Host permissions | In permissions | Separate field |
| Content scripts | executeScript string | executeScript files/func |
| CSP | Customizable | Restricted |
| Action | browser_action/page_action | action |

---

## Manifest Changes

### Basic Manifest Update

**MV2:**
```json
{
  "manifest_version": 2,
  "name": "My Extension",
  "version": "1.0",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "background": {
    "scripts": ["background.js"],
    "persistent": false
  },
  "permissions": [
    "tabs",
    "storage",
    "*://*.example.com/*"
  ]
}
```

**MV3:**
```json
{
  "manifest_version": 3,
  "name": "My Extension",
  "version": "1.0",
  "action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "background": {
    "service_worker": "background.js",
    "type": "module"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "host_permissions": [
    "*://*.example.com/*"
  ]
}
```

### Key Changes

1. `browser_action` / `page_action` → `action`
2. `background.scripts` → `background.service_worker`
3. Host permissions moved to `host_permissions`
4. Add `"type": "module"` for ES modules

---

## Background Page → Service Worker

### Key Differences

| Background Page | Service Worker |
|-----------------|----------------|
| Persistent (optional) | Always terminates |
| DOM access | No DOM |
| window object | No window |
| localStorage | No localStorage |
| XMLHttpRequest | fetch only |
| setTimeout reliable | setTimeout may not fire |

### Migration Steps

**1. Remove DOM dependencies:**

```javascript
// MV2 - Using DOM
const parser = new DOMParser();
const doc = parser.parseFromString(html, 'text/html