Web/JavaScript/Reference/Global objects/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

Specification
ECMAScript (ECMA-262)The definition of 'Object.isSealed' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`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