JavaScript (ES2026) reference · Object Methods

JavaScript Object.isSealed() Method

Return true if an object is sealed: properties can't be added or removed, but existing ones may still change.

JavaScript (ES2026) Since ES5

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Syntax

Object.isSealed(obj)

Parameter	Description
`obj`	The object to inspect or change.

true or false.

Sealed but not frozenTry it yourself

const s = Object.seal({ x: 1 });
console.log(Object.isSealed(s), Object.isFrozen(s));

Output

true false

Frozen objects are also sealedTry it yourself

console.log(Object.isSealed(Object.freeze({ y: 2 })));

Output

true

Version	Change
JavaScript ES5	Added

Object.seal() · Prevent adding or removing properties while still allowing existing properties to be changed.
Object.isFrozen() · Return true if an object is frozen: no properties can be added, removed or changed.
JavaScript Objects · tutorial