Object.freeze()

The Object.freeze() static method freezes an object. Freezing an object prevents extensions and makes existing properties non-writable and non-configurable. A frozen object can no longer be changed: new properties cannot be added, existing properties cannot be removed, their enumerability, configurability, writability, or value cannot be changed, and the object’s prototype cannot be re-assigned. freeze() returns the same object that was passed in.

Freezing an object is the highest integrity level that JavaScript provides.

Freezing an object is equivalent to preventing extensions and then changing all existing properties’ descriptors’ configurable to false — and for data properties, writable to false as well. Nothing can be added to or removed from the properties set of a frozen object. Any attempt to do so will fail, either silently or by throwing a TypeError exception (most commonly, but not exclusively, when in strict mode).

Syntax example: Object.freeze(obj)