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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.




The target object which to check if it is extensible.

Return value

A Boolean indicating whether or not the target is extensible.


A TypeError, if target is not an Object.


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().


Using Reflect.isExtensible()

See also Object.isExtensible().

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

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

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

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

Difference to Object.isExtensible()

If the first 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.

// TypeError: 1 is not an object

// false


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Reflect.isExtensible' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Reflect.isExtensible' in that specification.

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support 49 (Yes) 42 (42) No support No support 10
Feature Android Chrome for Android Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support 49 (Yes) 42.0 (42) No support No support 10

See also

Document Tags and Contributors

 Contributors to this page: jameshkramer, kdex, bsara, eduardoboucas, gingerik, fscholz, cmbankester
 Last updated by: jameshkramer,