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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

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
isExtensibleChrome Full support 49Edge Full support 12Firefox Full support 42IE No support NoOpera Full support 36Safari Full support 10WebView Android Full support 49Chrome Android Full support 49Firefox Android Full support 42Opera Android Full support 36Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0


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See also