The Object.isFrozen()
determines if an object is frozen.
Syntax
Object.isFrozen(obj)
Parameters
obj
- The object which should be checked.
Return value
A Boolean
indicating whether or not the given object is frozen.
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. Object.isFrozen({}); // === false // An empty object which is not extensible // is vacuously frozen. var vacuouslyFrozen = Object.preventExtensions({}); Object.isFrozen(vacuouslyFrozen); // === true // A new object with one property is also extensible, // ergo not frozen. var oneProp = { p: 42 }; 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); Object.isFrozen(oneProp); // === false // ...but then deleting that property makes the object // vacuously frozen. delete oneProp.p; 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 Object.isFrozen(nonWritable); // === false // Changing that property to non-configurable // then makes the object frozen. Object.defineProperty(nonWritable, 'e', { configurable: false }); // make non-configurable 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 }); Object.isFrozen(nonConfigurable); // === false // Changing that property to non-writable // then makes the object frozen. Object.defineProperty(nonConfigurable, 'release', { writable: false }); 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); Object.isFrozen(accessor); // === false // ...but make that property non-configurable // and it becomes frozen. Object.defineProperty(accessor, 'food', { configurable: false }); 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 }; Object.isFrozen(frozen); // === false Object.freeze(frozen); Object.isFrozen(frozen); // === true // By definition, a frozen object is non-extensible. Object.isExtensible(frozen); // === false // Also by definition, a frozen object is sealed. 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 ES2015, 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 (ES2015 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 | |
ECMAScript Latest Draft (ECMA-262) The definition of 'Object.isFrozen' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | 6 | (Yes) | 4.0 (2.0) | 9 | 12 | 5.1 |
Feature | Android | Chrome for Android | Edge | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|
Basic support | ? | ? | (Yes) | ? | ? | ? | ? |
See also
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Last updated by:
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