Web/JavaScript/Reference/Global objects/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.

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

Specification
ECMAScript (ECMA-262)The definition of 'Reflect.isExtensible' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`isExtensible`	Chrome Full support 49	Edge Full support 12	Firefox Full support 42	IE No support No	Opera Full support 36	Safari Full support 10	WebView Android Full support 49	Chrome Android Full support 49	Firefox Android Full support 42	Opera Android Full support 36	Safari iOS Full support 10	Samsung Internet Android Full support 5.0	nodejs Full support 6.0.0

Legend

Full support: Full support
No support: No support