JavaScript Object.isExtensible()

Definition and usage

Object.isExtensible() The method is used to check if an object is extensible. If the object is extensible, it returns true.

Related methods:

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

Object.seal() Modification is allowed, but addition and deletion of properties are 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 return false
let answer = Object.isExtensible(person);

Try it yourself

Example 2

// Create an array
const fruits = ["Banana", "Orange", "Apple", "Mango"];
// Prevent extension
Object.preventExtensions(fruits);
// This will return false
let answer = Object.isExtensible(fruits);

Try it yourself

Syntax

Object.isExtensible(object)

Parameter

Return value

Browser support

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

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