Last Updated : 12 Jul, 2025
The Object.preventExtensions() method in JavaScript is a standard built-in object which checks whether an object is extensible or not(i.e. if we can add new properties to the object or not).
Syntax:
Object.isExtensible( obj )
Parameters: This method accepts a single parameter as mentioned above and described below:
Return value: This method returns a Boolean value indicating if the given object is extensible or not.
The below examples illustrate the Object.isExtensible() Method in JavaScript:
Example 1: In this example, we will check if new properties can be added to an object or not using the Object.isExtensible() Method in JavaScript. The output is a Boolean value.
javascript
const geeks1 = {};
console.log(Object.isExtensible(geeks1));
Object.preventExtensions(geeks1);
console.log(Object.isExtensible(geeks1));
const geeks2 = {};
Object.preventExtensions(geeks2);
console.log(
Object.isExtensible(geeks2)
);
Output:
true false false
Example 2: In this example, we will check if new properties can be added to an object or not using the Object.isExtensible() Method in JavaScript. The output is a Boolean value.
javascript
let geeks1 = {};
console.log(Object.isExtensible(geeks1));
console.log(Object.preventExtensions(geeks1));
console.log(Object.isExtensible(geeks1));
let geeks2 = Object.seal({});
console.log(Object.isExtensible(geeks2));
let geeks3 = Object.freeze({});
console.log(Object.isExtensible(geeks3));
Output:
true [object Object] false false false
We have a complete list of Javascript Object methods, to check those please go through this JavaScript Object Complete Reference article.
Supported Browsers: The browsers supported by Object.isExtensible() method are listed below:
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