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Object.isExtensible Redirect 1

Summary

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

Syntax

Object.isExtensible(obj)

Parameters

obj
The object which should be checked.

Description

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.

Examples

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

// ...but that can be changed.
Object.preventExtensions(empty);
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);

Specifications

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.
Draft  

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

Contributors to this page: Sheppy
Last updated by: Sheppy,