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Object.isExtensible Redirect 1


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




The object which should be checked.


Objects are extensible by default: they can have new properties added to them, and (in engines that support __proto__ their __proto__ property) can be modified. An object can be marked as non-extensible using Object.preventExtensions, Object.seal, or Object.freeze.


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

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

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

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


Specification Status Comment
ECMAScript 5.1 (ECMA-262)
The definition of 'Object.isExtensible' in that specification.
Standard Initial definition.
Implemented in JavaScript 1.8.5
ECMAScript 6 (ECMA-262)
The definition of 'Object.isExtensible' in that specification.

Browser compatibility

Feature Firefox (Gecko) Chrome Internet Explorer Opera Safari
Basic support 4 (2.0) 6 9 12 5.1
Feature Firefox Mobile (Gecko) Android IE Mobile Opera Mobile Safari Mobile
Basic support ? ? ? ? ?

Based on Kangax's compat table.

See also

Document Tags and Contributors

 Last updated by: Sheppy,