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# Object.isExtensible()

The **`Object.isExtensible()`** method determines if an object
is extensible (whether it can have new properties added to it).

## Syntax

```js
Object.isExtensible(obj)
```

### Parameters

- `obj`
  - : The object which should be checked.

### Return value

A `Boolean` indicating whether or not the given object is extensible.

## Description

Objects are extensible by default: they can have new properties added to them, and their `[[Prototype]]` can be re-assigned. An object can be marked as non-extensible using one of [`Object.preventExtensions()`](../../globals/Object/preventExtensions.mdx), [`Object.seal()`](../../globals/Object/seal.mdx), [`Object.freeze()`](../../globals/Object/freeze.mdx), or [`Reflect.preventExtensions()`](../../globals/Reflect/preventExtensions.mdx).
