👁️ MutationObserver: Watching DOM Changes in JavaScript
Category: js / general-concepts
Difficulty: medium
MutationObserver is a powerful Web API that lets you watch for changes in the DOM — whenever elements are added, removed, modified, or their attributes change. It's like having a security camera for your DOM tree. 💡 What Is MutationObserver? MutationObserver is a built-in browser API that allows you to detect and react to mutations (changes) in the DOM without constantly polling or checking the DOM manually. Why do you need it? Detect when external code modifies the DOM Auto-update UI based on structural changes Debug unexpected DOM mutations Build reactive components Monitor third-party scripts or dynamic content 🧠 Core Concepts MutationObserver Constructor [code example] Starting Observation with .observe() [code example] Stopping Observation with .disconnect() [code example] Getting Pending Mutations [code example] 🧪 Basic Example: Watch for Child Changes [code example] 🧪 Use Case 1: Monitor Text Content Changes [code example] 🧪 Use Case 2: Detect Attribute Modifications [code example] 🧪 Use Case 3: Detect Deep Subtree Changes Watch an entire element tree for any changes: [code example] 🧪 Use Case 4: Auto-Highlight New Elements [code example] 🧪 Use Case 5: Track Form Input Changes Detect when form fields are dynamically modified: [code example] 🧪 Use Case 6: Detect Image Load Completion [code example] 🧪 Use Case 7: Implement Auto-Save on DOM Changes [code example] 🧪 Use Case 8: Detect Third-Party Script Injections Monitor for unauthorized DOM modifications: [code example] 🧪 Use Case 9: MutationRecord Structure Understanding what information is available in each mutation: [code example] 🧪 Use Case 10: Performance Monitoring with MutationObserver Track DOM manipulation performance: [code example] 🧪 Real-World Example: Dynamic List Manager A complete, practical example: [code example] 📋 Configuration Options Reference Type boolean boolean boolean string[] boolean boolean boolean ⚠️ Performance Considerations Don't Watch Everything [code example] Use a...