Object.seal() prevents adding or deleting properties but allows modifying existing properties. It’s less restrictive than Object.freeze().

const user = Object.seal({ name: 'Alice', age: 25 });

user.age = 26;     // ✅ Allowed — modification
user.email = 'a@b.com'; // ❌ Cannot add
delete user.name;  // ❌ Cannot delete
Object.isSealed(user); // true

• Object.seal() prevents add/delete but allows modification
• Use when you want to prevent structural changes but allow value updates
• Check with Object.isSealed()

• MDN: Object.seal()