The Object.isSealed()
method determines if an object is sealed.
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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
Using Object.isSealed
// 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)
Non-object coercion
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
.
Object.isSealed(1); // TypeError: 1 is not an object (ES5 code) Object.isSealed(1); // true (ES2015 code)
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Object.isSealed' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
isSealed | Chrome Full support 6 | Edge Full support 12 | Firefox Full support 4 | IE Full support 9 | Opera Full support 12 | Safari Full support 5.1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 12 | Safari iOS Full support 6 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support