Javascript Object.isFrozen()

let obj = {name: "JavaScript"};

// new objects are extensible, so they're not frozen
console.log(Object.isFrozen(obj)); 

// Output: false

isFrozen() syntax

The syntax of the isFrozen() method is:

Object.isFrozen(obj)

Here, isFrozen() is a static method. Hence, we need to access the method using the class name, Object.

isFrozen() Parameters

The isFrozen() method takes in:

• obj - the object which should be checked for being frozen or not.

isFrozen() Return Value

The isFrozen() method returns:

• true - if the object is frozen
• false - if the object is not frozen

Example: Javascript Object.isFrozen()

let newObj = { b: 2 };

// preventing extensions doesn't freeze an object
// since its properties are still configurable
Object.preventExtensions(newObj);

// check if newObj is frozen
console.log(Object.isFrozen(newObj));

// Output: false

// make newObj non-writable
Object.defineProperty(newObj, "b", {
  writable: false,
});

// object is not frozen
console.log(Object.isFrozen(newObj));

// Output: false

// use the freeze() method
Object.freeze(newObj);

// object is finally frozen
console.log(Object.isFrozen(newObj));

// Output: true

In the above example, we tried to freeze newObj by

• using the preventExtensions() method, and
• making it unwritable by setting the writable flag to false.

However, both approaches fail to freeze the object.

The final output indicates that newObj is frozen only after calling the freeze() method.

Recommended Reading:

• JavaScript Object.freeze()