The Object.isExtensible()
method determines if an object is extensible (whether it can have new properties added to it).
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Syntax
Object.isExtensible(obj)
Parameters
obj
- The object which should be checked.
Return value
A Boolean
indicating whether or not the given object is extensible.
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
Using Object.isExtensible
// New objects are extensible. var empty = {}; Object.isExtensible(empty); // === true // ...but that can be changed. Object.preventExtensions(empty); Object.isExtensible(empty); // === false // Sealed objects are by definition non-extensible. var sealed = Object.seal({}); Object.isExtensible(sealed); // === false // Frozen objects are also by definition non-extensible. var frozen = Object.freeze({}); Object.isExtensible(frozen); // === false
Non-object coercion
In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError
. In ES2015, a non-object argument will be treated as if it was a non-extensible ordinary object, simply return false
.
Object.isExtensible(1); // TypeError: 1 is not an object (ES5 code) Object.isExtensible(1); // false (ES2015 code)
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Object.isExtensible' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
isExtensible | Chrome Full support 6 | Edge Full support 12 | Firefox Full support 4 | IE Full support 9 | Opera Full support 12 | Safari Full support 5.1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 12 | Safari iOS Full support 6 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support