How to make a property or a method in an object immutable in JavaScript?

Published June 19, 2020

Let's say you have an object called John.

const John = {};

Now we can add the name property and assign it a value of John Doe and also make it a not changing or immutable property.

We can acheive this through the Object.defineProperty() static method.

const John = {};

// setting property name: "John Doe"
// and also making it immutable
Object.defineProperty(John, "name", {
  value: "John Doe",
  writable: false,
});

The method accepts:

  • The object to add the property as the first parameter, in our case John.
  • The name of the property you want to add to the object as the second parameter, in our case the name property.
  • The third parameter is called descriptor where we are setting the value option to the value we want in our name property in our case "John Doe" and writable property to false for making it immutable.

Now if you try to change the value of the name in object John, It will throw an error in strict mode.

// will throw an error
John.name = "Lily";

There are many other options you can set in the descriptor including writable, enumerable, and configurable.

Check more about these options in MDN Docs

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