Actually, JavaScript uses a different approach than C# or C++ to create an object-oriented language. It is a prototype-based language.

With the exception of JavaScript, prototypal inheritance is not part of any mainstream language. To make matters worse, it’s possible to emulate the classical model in JavaScript.

Such prototypal inheritance can effectively mimic class-based inheritance, without creating classes, in more than one way. See Dean Edwards’ base2, qooxdoo, Prototype for a few implementations.