Our volunteers haven't translated this article into Tiếng Việt yet. Join us and help get the job done!
The Object.isSealed()
method determines if an object is sealed.
Syntax
Object.isSealed(obj)
Parameters
obj
- The object which should be checked.
Return value
A Boolean
indicating whether or not the given object is sealed.
Description
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).
Examples
// 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.preventExtensions(empty); 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.preventExtensions(hasProp); 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.seal(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)
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 sealed ordinary object, simply return true
.
Object.isSealed(1); // TypeError: 1 is not an object (ES5 code) Object.isSealed(1); // true (ES6 code)
Specifications
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. |
Standard | |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Object.isSealed' in that specification. |
Draft |
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 | ? | ? | ? | ? | ? | ? |
See also
Document Tags and Contributors
Tags:
Contributors to this page:
eduardoboucas,
fscholz,
claudepache,
Mingun,
ziyunfei,
Sheppy,
ethertank,
dbruant,
JamesWatts,
evilpie,
Waldo,
Crash
Last updated by:
eduardoboucas,