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    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);


    In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError. In ES6, 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                         // ES6 code


    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.
    Release Candidate  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support 6 4.0 (2.0) 9 12 5.1
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support ? ? ? ? ? ?

    Based on Kangax's compat table.

    See also

    Document Tags and Contributors

    Last updated by: Mingun,