Object.isSealed()

{{JSRef}}

The Object.isSealed() static method determines if an object is sealed.

{{InteractiveExample("JavaScript Demo: Object.isSealed()")}}

const object1 = {
  property1: 42,
};

console.log(Object.isSealed(object1));
// Expected output: false

Object.seal(object1);

console.log(Object.isSealed(object1));
// Expected output: true

Syntax

Object.isSealed(obj)

Parameters

obj
- : The object which should be checked.

Return value

A {{jsxref("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 {{jsxref("Object/isExtensible", "extensible", "", 1)}} 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.
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)

Non-object argument

In ES5, if the argument to this method is not an object (a primitive), then it will cause a {{jsxref("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)

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

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