I am relatively new to JavaScript and keep seeing .extend and .prototype in third party libraries I am using. I thought it had to do with the Prototype javascript library, but I am beginning to think that is not the case. What are these used for?
Javascript's inheritance is prototype based, so you extend the prototypes of objects such as Date, Math, and even your own custom ones.
Date.prototype.lol = function() {
alert('hi');
};
( new Date ).lol() // alert message
In the snippet above, I define a method for all Date objects ( already existing ones and all new ones ).
extend is usually a high level function that copies the prototype of a new subclass that you want to extend from the base class.
So you can do something like:
extend( Fighter, Human )
And the Fighter constructor/object will inherit the prototype of Human, so if you define methods such as live and die on Human then Fighter will also inherit those.
Updated Clarification:
"high level function" meaning .extend isn't built-in but often provided by a library such as jQuery or Prototype.