🛡️ JavaScript Object Protection

📌 1. Why Protect Objects?

• Prevent accidental changes
• Secure data from tampering
• Lock configuration/settings
• Improve code stability and debugging

✅ 2. Protection Levels in JavaScript

🔒 3. Object.preventExtensions()

Prevents adding new properties, but existing ones can still be changed or deleted.

jsCopyEditconst user = { name: "Alice" };
Object.preventExtensions(user);

user.age = 30;           // ❌ Won't add
console.log(user.age);   // undefined

user.name = "Bob";       // ✅ Allowed
delete user.name;        // ✅ Allowed

🔐 4. Object.seal()

Prevents adding or deleting properties. Values can still be modified.

jsCopyEditconst user = { name: "Alice" };
Object.seal(user);

user.age = 30;           // ❌ Won't add
delete user.name;        // ❌ Won't delete

user.name = "Bob";       // ✅ Can update value

🧊 5. Object.freeze()

Makes the object completely immutable: can’t add, delete, or change properties.

jsCopyEditconst config = {
  apiKey: "12345"
};
Object.freeze(config);

config.apiKey = "54321";  // ❌ No change
config.url = "api.com";   // ❌ Won't add
delete config.apiKey;     // ❌ Won't delete

🔍 Object.freeze() is shallow: it only applies to the top-level properties. To deep-freeze, you must recursively freeze nested objects.

📌 6. Checking Protection State

jsCopyEditObject.isExtensible(obj); // false if preventExtensions used
Object.isSealed(obj);     // true if sealed
Object.isFrozen(obj);     // true if frozen

🔄 7. Deep Freezing Utility Function

jsCopyEditfunction deepFreeze(obj) {
  Object.getOwnPropertyNames(obj).forEach(name => {
    const value = obj[name];
    if (value && typeof value === "object") {
      deepFreeze(value);
    }
  });
  return Object.freeze(obj);
}

// Usage
const settings = {
  server: {
    host: "localhost",
    port: 8080
  }
};

deepFreeze(settings);
settings.server.port = 3000; // ❌ Won't change

🧪 Practice Challenge

Create an object bankAccount:

• With properties: owner, balance
• Use Object.seal() to prevent property removal or addition
• Add a method deposit(amount) to increase balance

💡 Summary Table

Would you like:

• 🧪 Interactive sandbox or playground?
• 📄 Downloadable PDF version?
• ✅ Quiz on object protection methods?