subclass.prototype = new superclass() vs. subclass = new superclass()

Question

I\'ve been instantiating subclasses in javascript using

object = new class ()

but I notice some people instantiate using

ob         


        

Answer 1

The difference is that when you do:

var subclass = new superclass();

you are creating an instance of superclass. subclass is just variable. You are not creating a sub-class (ie. making subclass inherit superclass). In the latter example, assuming subclass is a function, you are saying that all new instances of subclass should inherit (ie. sub-class) superclass.

So:

function superclass() {this.stuff="stuff";}
function subclass() {}
subclass.prototype = new superclass();
alert(new subclass().this); // pops up "stuff"

is prototypical inheritance.

As for the new operator, it is used for creating an instance of built-in objects and user defined types. A user defined type is simply a function.

Edit: When I wrote above that subclass inherits supertype using prototypical inheritance, I mean that all new instances of subclass inherit from one particular instance of superclass, not from the superclass type/function itself.