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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

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
isSealedChrome Full support 6Edge Full support 12Firefox Full support 4IE Full support 9Opera Full support 12Safari Full support 5.1WebView Android Full support YesChrome Android Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes


Full support  
Full support

See also