The Object.isSealed()
static method determines if an object is sealed.
The Object.isSealed()
static method determines if an object is sealed.
Object.isSealed(obj)
obj
The object which should be checked.
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. const 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. const 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. const 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) const s2 = Object.seal({ p: 3 }); Object.isFrozen(s2); // false // ('p' is still writable) const 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, it will return true
without any errors if a non-object argument is passed, since primitives are, by definition, immutable.
Object.isSealed(1); // TypeError: 1 is not an object (ES5 code) Object.isSealed(1); // true (ES2015 code)
Specification |
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ECMAScript Language Specification # sec-object.issealed |
Desktop | Mobile | Server | ||||||||||||
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Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | Deno | Node.js | ||
isSealed |
6 | 12 | 4 | 12 | 5.1 | 18 | 4 | 12 | 5 | 1.0 | 4.4 | 1.0 | 0.10.0 |
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isSealed