The encapsulation is enforced by the language. It is a syntax error to refer to # names from out of scope.

in languages (like JavaScript and Java) where external objects do have direct access to instance vars

Note: there’s no way to define private methods, getters and setters. but a proposal is there https://github.com/tc39/proposal-private-methods

Private instance accessors (getters and setters)

class Person { #firstname = "Babel"; #lastname = "JS"; get #name() { return this.#firstname + " " + this.#lastname; } sayHi() { alert(`Hi, ${this.#name}!`); } }