Using classes hasn't been a part of the definition of OOP since the Treaty of Orlando. Pre-ECMAScript-2015 JS is a mainstream OOP language that doesn't have classes, just prototypes. (Arguably ECMAScript 2015 classes aren't really classes either.)
It sounds funny to say that JavaScript classes aren't classes, but if you don't believe me, just ask JavaScript in your browser (Ctrl-Alt-K, probably):
Using classes hasn't been a part of the definition of OOP since the Treaty of Orlando. Pre-ECMAScript-2015 JS is a mainstream OOP language that doesn't have classes, just prototypes. (Arguably ECMAScript 2015 classes aren't really classes either.)