JavaScript Object.preventExtensions()

Definition and usage

Object.preventExtensions() method to prevent adding new properties to an object.

You can use Object.isExtensible() to check if an object is extensible.

Related methods:

Object.preventExtensions() Modification is allowed, but adding properties is prevented.

Object.seal() Modification is allowed, but adding and deleting properties is prevented.

Object.freeze() Prevent modification, addition, and deletion of properties.

Object.isExtensible() Returns true if the object is extensible.

Object.isSealed() Returns true if the object is sealed.

Object.isFrozen() Returns true if the object is frozen.

Instance

Example 1

// Create an object
const person = {firstName: "Bill", lastName: "Gates"};
// Prevent extension
Object.preventExtensions(person);
// This will throw an error in strict mode
person.nationality = "English";

Try It Yourself

Example 2

// Create an array
const fruits = ["Banana", "Orange", "Apple", "Mango"];
Object.preventExtensions(fruits);
// This will throw an error in strict mode:
fruits.push("Kiwi");

Try It Yourself

Syntax

Object.preventExtensions(object)

Parameter

Return Value

Browser Support

Object.preventExtensions() Is a feature of ECMAScript5 (ES5).

Since July 2013, all modern browsers have fully supported ES5 (JavaScript 2009):