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    Object.isFrozen()

    Summary

    The Object.isFrozen() determines if an object is frozen.

    Syntax

    Object.isFrozen(obj)

    Parameters

    obj
    The object which should be checked.

    Description

    An object is frozen if and only if it is not extensible, all its properties are non-configurable, and all its data properties (that is, properties which are not accessor properties with getter or setter components) are non-writable.

    Examples

    // A new object is extensible, so it is not frozen.
    assert(Object.isFrozen({}) === false);
    
    // An empty object which is not extensible is vacuously frozen.
    var vacuouslyFrozen = Object.preventExtensions({});
    assert(Object.isFrozen(vacuouslyFrozen) === true);
    
    // A new object with one property is also extensible, ergo not frozen.
    var oneProp = { p: 42 };
    assert(Object.isFrozen(oneProp) === false);
    
    // Preventing extensions to the object still doesn't make it frozen,
    // because the property is still configurable (and writable).
    Object.preventExtensions(oneProp);
    assert(Object.isFrozen(oneProp) === false);
    
    // ...but then deleting that property makes the object vacuously frozen.
    delete oneProp.p;
    assert(Object.isFrozen(oneProp) === true);
    
    // A non-extensible object with a non-writable but still configurable property is not frozen.
    var nonWritable = { e: 'plep' };
    Object.preventExtensions(nonWritable);
    Object.defineProperty(nonWritable, 'e', { writable: false }); // make non-writable
    assert(Object.isFrozen(nonWritable) === false);
    
    // Changing that property to non-configurable then makes the object frozen.
    Object.defineProperty(nonWritable, 'e', { configurable: false }); // make non-configurable
    assert(Object.isFrozen(nonWritable) === true);
    
    // A non-extensible object with a non-configurable but still writable property also isn't frozen.
    var nonConfigurable = { release: 'the kraken!' };
    Object.preventExtensions(nonConfigurable);
    Object.defineProperty(nonConfigurable, 'release', { configurable: false });
    assert(Object.isFrozen(nonConfigurable) === false);
    
    // Changing that property to non-writable then makes the object frozen.
    Object.defineProperty(nonConfigurable, 'release', { writable: false });
    assert(Object.isFrozen(nonConfigurable) === true);
    
    // A non-extensible object with a configurable accessor property isn't frozen.
    var accessor = { get food() { return 'yum'; } };
    Object.preventExtensions(accessor);
    assert(Object.isFrozen(accessor) === false);
    
    // ...but make that property non-configurable and it becomes frozen.
    Object.defineProperty(accessor, 'food', { configurable: false });
    assert(Object.isFrozen(accessor) === true);
    
    // But the easiest way for an object to be frozen is if Object.freeze has been called on it.
    var frozen = { 1: 81 };
    assert(Object.isFrozen(frozen) === false);
    Object.freeze(frozen);
    assert(Object.isFrozen(frozen) === true);
    
    // By definition, a frozen object is non-extensible.
    assert(Object.isExtensible(frozen) === false);
    
    // Also by definition, a frozen object is sealed.
    assert(Object.isSealed(frozen) === true);
    

    Notes

    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 frozen ordinary object, simply return true.

    > Object.isFrozen(1)
    TypeError: 1 is not an object // ES5 code
    
    > Object.isFrozen(1)
    true                          // ES6 code
    

    Specifications

    Specification Status Comment
    ECMAScript 5.1 (ECMA-262)
    The definition of 'Object.isFrozen' in that specification.
    Standard Initial definition. Implemented in JavaScript 1.8.5.
    ECMAScript 2015 (6th Edition, ECMA-262)
    The definition of 'Object.isFrozen' in that specification.
    Standard  

    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: claudepache,