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Explain the difference between mutable and immutable objects in JavaScript

By FrontendPro Editorial Team Updated 8/8/2026

#JavaScript

Answer

Mutable objects allow for modification of properties and values after creation, which is the default behavior for most objects.

const mutableObject = {
  name: "John",
  age: 30,
};

// Modify the object
mutableObject.name = "Jane";

// The object has been modified
console.log(mutableObject); // Output: { name: 'Jane', age: 30 }

Immutable objects cannot be directly modified after creation. Their contents cannot be changed without creating an entirely new value.

const immutableObject = Object.freeze({
  name: "John",
  age: 30,
});

// Attempt to modify the object
immutableObject.name = "Jane";

// The object remains unchanged
console.log(immutableObject); // Output: { name: 'John', age: 30 }

The key difference between mutable and immutable objects is modifiability. Immutable objects cannot be modified after they are created, while mutable objects can be.