Writing classes in JavaScript doesn't give full functionality of an object oriented language, but it at least gives data hiding and encapsulation which are very useful specially when JavaScript is not a strongly typed language. It is very useful in cases when you need to handle multiple objects , instead of having arrays for all kinds of variables and then managing those arrays in methods you can just write a class to handle one object and then make many instances of that class. This also gives the name space resolution to the variables so that you can avoid using global variables and still use variables across procedures.