Object.freeze()

Object.freeze() is a method that freezes an object, making it immutable. This means that the properties of the object cannot be added, deleted, or modified. All nested objects a is still mutable.

Syntax

Object.freeze(obj)

Parameter

• obj: The object to be frozen.

Return Value

Object.freeze() returns the same object that was passed as a parameter after it has been frozen.

Examples

Example 1:

const obj = { x: 1, y: 2, z: 3 };
Object.freeze(obj);

obj.x = 5;
console.log(obj); // Output: { x: 1, y: 2, z: 3 }

In this example, Object.freeze() is used to freeze the obj object, making it immutable. When an attempt is made to modify the x property of the obj object, no changes are made to the object.

Example 2:

const obj = { a: { b: 2 } };
Object.freeze(obj);

obj.a.b = 3;
console.log(obj); // Output: { a: { b: 3 } }

In this example, Object.freeze() is used to freeze the obj object, but the nested object a is still mutable. When an attempt is made to modify the b property of the a object, the object is modified successfully.

Notes

• Object.freeze() makes an object read-only, but it does not make the properties of the object themselves read-only. If the properties of the object are objects, they can still be modified.

• If Object.freeze() is called on a non-object value, an error will be thrown.

• The Object.isFrozen() method can be used to determine whether an object is frozen or not.

Exercises

1. Write a function that takes an object as an argument and returns a frozen version of the object.

2. Use Object.freeze() to create a constant object that cannot be modified.

3. Write a function that takes an array of objects as an argument and freezes all the objects in the array using Object.freeze().

function freezeObject(obj) {
  return Object.freeze(obj);
}

const obj = { x: 1, y: 2, z: 3 };
const frozenObj = freezeObject(obj);

console.log(frozenObj); // Output: { x: 1, y: 2, z: 3 }

const MY_CONSTANT = Object.freeze({ x: 1, y: 2, z: 3 });

function freezeObjects(arr) {
  arr.forEach(obj => Object.freeze(obj));
}

const arr = [{ x: 1 }, { y: 2 }, { z: 3 }];
freezeObjects(arr);

arr[0].x = 5;
console.log(arr); // Output: [{ x: 1 }, { y: 2 }, { z: 3 }]