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The Object.isSealed() method determines if an object is sealed.




The object which should be checked.

Return value

A Boolean indicating whether or not the given object is sealed.


Returns true if the object is sealed, otherwise false. An object is sealed if it is not extensible and if all its properties are non-configurable and therefore not removable (but not necessarily non-writable).


// Objects aren't sealed by default.
var empty = {};
Object.isSealed(empty); // === false

// If you make an empty object non-extensible,
// it is vacuously sealed.
Object.isSealed(empty); // === true

// The same is not true of a non-empty object,
// unless its properties are all non-configurable.
var hasProp = { fee: 'fie foe fum' };
Object.isSealed(hasProp); // === false

// But make them all non-configurable
// and the object becomes sealed.
Object.defineProperty(hasProp, 'fee', {
  configurable: false
Object.isSealed(hasProp); // === true

// The easiest way to seal an object, of course,
// is Object.seal.
var sealed = {};
Object.isSealed(sealed); // === true

// A sealed object is, by definition, non-extensible.
Object.isExtensible(sealed); // === false

// A sealed object might be frozen,
// but it doesn't have to be.
Object.isFrozen(sealed); // === true 
// (all properties also non-writable)

var s2 = Object.seal({ p: 3 });
Object.isFrozen(s2); // === false 
// ('p' is still writable)

var s3 = Object.seal({ get p() { return 0; } });
Object.isFrozen(s3); // === true
// (only configurability matters for accessor properties)


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 sealed ordinary object, simply return true.

// TypeError: 1 is not an object (ES5 code)

// true                          (ES2015 code)


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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support6 Yes49125.1
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support Yes Yes Yes Yes Yes Yes ?

See also

Etiquetas y colaboradores del documento

 Última actualización por: wbamberg,