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Object.isSealed

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

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

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
isSealed 6 12 4 9 12 5.1
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
isSealed 1 18 4 12 6 1.0
Server
Node.js
isSealed Yes

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isSealed