javascript / latest / global_objects / reflect / isextensible.html /

Reflect.isExtensible()

The static Reflect.isExtensible() method determines if an object is extensible (whether it can have new properties added to it). It is similar to Object.isExtensible(), but with some differences.

Try it

Syntax

Reflect.isExtensible(target)

Parameters

target

The target object which to check if it is extensible.

Return value

A Boolean indicating whether or not the target is extensible.

Exceptions

A TypeError, if target is not an Object.

Description

The Reflect.isExtensible method allows you determine if an object is extensible (whether it can have new properties added to it). It is the same method as Object.isExtensible().

Examples

Using Reflect.isExtensible()

See also Object.isExtensible().

// New objects are extensible.
let empty = {}
Reflect.isExtensible(empty)  // === true

// ...but that can be changed.
Reflect.preventExtensions(empty)
Reflect.isExtensible(empty)  // === false

// Sealed objects are by definition non-extensible.
let sealed = Object.seal({})
Reflect.isExtensible(sealed)  // === false

// Frozen objects are also by definition non-extensible.
let frozen = Object.freeze({})
Reflect.isExtensible(frozen)  // === false

Difference to Object.isExtensible()

If the target argument to this method is not an object (a primitive), then it will cause a TypeError. With Object.isExtensible(), a non-object first argument will be coerced to an object at first.

Reflect.isExtensible(1)
// TypeError: 1 is not an object

Object.isExtensible(1)
// false

Specifications

Browser compatibility

Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet Deno Node.js
isExtensible
49
12
42
No
36
10
49
49
42
36
10
5.0
1.0
6.0.0

See also

© 2005–2022 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Reflect/isExtensible