Mutable and non-mutable data types in JavaScript ?

Question

In the below article it is written that "objects & classes" are mutable.
But as far as I know there is no such concept like "classes" in JavaScript.
Also "objects" includes arrays, functions etc. then why are "objects" explicitly classified in mutable category.

LINK:
https://benmccormick.org/2016/06/04/what-are-mutable-and-immutable-data-structures-2

Answer 1

Btw. ES6 introduced classes.
Every object in JS is mutable. You can always add and change members. Even const objects are mutable.