# The Object isExtensible() method

> Learn how the JavaScript Object.isExtensible() method checks if you can add properties to an object, returning false after freeze, seal, or preventExtensions.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2019-04-09 | Topics: [JavaScript](https://flaviocopes.com/tags/js/) | Canonical: https://flaviocopes.com/javascript-object-isextensible/

This method checks if we can add new properties to an object.

Any object is extensible, unless it's been used as an argument to

- [`Object.freeze()`](https://flaviocopes.com/javascript-object-freeze/)
- [`Object.seal()`](https://flaviocopes.com/javascript-object-seal/)
- [`Object.preventExtensions()`](https://flaviocopes.com/javascript-object-preventextensions/)

Usage:

```js
const dog = {}
Object.isExtensible(dog) //true
```

```js
const cat = {}
Object.freeze(cat)
Object.isExtensible(cat) //false
```