JavaScript (ES2026) reference · Object Methods

JavaScript Object.seal() Method

Prevent adding or removing properties while still allowing existing properties to be changed.

JavaScript (ES2026) Since ES5

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Syntax

Object.seal(obj)

Parameters

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

Return value

The same object, now sealed.

Examples

Change, but not addTry it yourself

"use strict";
const point = Object.seal({ x: 1, y: 2 });
point.x = 10;
try { point.z = 3; } catch (e) { console.log(e.constructor.name); }
console.log(point);

Output

TypeError
{ x: 10, y: 2 }

Deleting failsTry it yourself

const p = Object.seal({ a: 1 });
try {
  delete p.a; // examples run as modules, which are strict mode
} catch (e) {
  console.log(e.constructor.name);
}
console.log(p);