The JavaScript freeze() method of the Object object takes an object as argument, and returns the same object. The object passed as argument is mutated and it’s now an immutable object. No properties can be added, no properties can be removed, properties can’t be changed.

Example:

const dog = {}
dog.breed = 'Siberian Husky'
const myDog = Object.freeze(dog)

Object.isFrozen(dog) //true
Object.isFrozen(myDog) //true
dog === myDog //true

dog.name = 'Roger' //TypeError: Cannot add property name, object is not extensible

Also see Object.isFrozen()

In the example, both dog and myDog are frozen. The argument passed as argument to Object.freeze() is mutated, and can’t be un-freezed. It’s also returned as argument, hence dog === myDog (it’s the same exact object).

Calling Object.freeze() is the equivalent of calling Object.preventExtensions() to prevent an object to have more properties defined, plus setting all properties as non-configurable and non-writeable.