How to make an object immutable in JavaScript?

Published June 21, 2020

To make an object read only or immutable you can use the Object.freeze() method.

Consider this object,

const Car = {
  name: "Audi",
  year: "2020",
};

We don't want any more properties to be added to this Car object.

Let's use the Object.freeze() method to achieve this.

const Car = {
  name: "Audi",
  year: "2020",
};

// make car object immutable
Object.freeze(Car);

Now if you try to add or change any properties in the Car object, it will throw an error in strict mode.

const Car = {
  name: "Audi",
  year: "2020",
};

// make car object immutable
Object.freeze(Car);

// try to add a new property
Car.engineType = "BS-VI"; // error in strict mode

• The Object.freeze() method accepts the object to make it immutable as the parameter.
• The method returns the same object which is passed into it.
• Cannot add or modify any properties and methods after calling the method.
• It also restricts any modification to the prototype.

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