Under the section "The Property (object attribute)" the code segment has two curious lines. I expect the first cancels out the latter, making the latter useless.

     // in Person function
     this.gender = gender;
     // outer scope (gender will never be this value because it is overridden by the person constructor argument)
     Person.prototype.gender = 'Person Gender';

Am I correct, or does the prototype.gender line have some other purpose than instantiating gender to a value that is immediately overridden by the passed in value (or undefined if no value is passed)?

It's ensuring a default value basically. If you instantiate a person without an argument and try to reference this.gender later, you'll throw a script error. This is just avoiding that.

A way I'd prefer might look like this:

  function Person = function(gender) {
      this.gender = gender || 'neuter' //the sauce that defines a fallback
  }

This is not the case, because in the constructor person is being set to the argument. If the argument is not supplied (undefined), calling the instantiated object's gender property will result in undefined. [tested and confirmed]

Presumably if the gender property is deleted the prototype.gender will come through

Might want to check the Joose object system (http://joose.it/ #joose on irc.freenode.net), highly inspired in the awesome thing that Moose (http://search.cpan.org/dist/Moose/) is to Perl. There's even a port of KiokuDB as KiokuJS!(http://joose.it/blog/2011/01/13/introducing-kiokujs/) :)

It's good to know this stuff, but in my real-world usage of JavaScript, I've become a big fan of Backbone.js to help structure code intelligently, etc.

> Inheritance A Class can inherit characteristics from another Class.

Somebody should tell Mozilla, that there are no classes in JavaScript....

The document is probably targeted at newcomers from other languages. But still…

The guide says that immediately after the terminology paragraph

But comes back to it at the Custom Objects part(1). And everywhere. They don't use "class" as a keyword, though, but more in a CS way which can be problematic because other keywords like "prototype", "array" or "object" mean pretty much the same thing in both contexts.

An interesting ressource, anyway.

(1) https://developer.mozilla.org/en/Introduction_to_Object-Orie...

Please don't make us start saying "object used as a class".

The first step to learning JavaScript is to forget about class-ical OOP, you can't write good code if you start forcing class-ical concepts on JavaScript, it's a prototypical language encouraging people to treat it as something else is wrong.

When a language has a deficiency people make up for it with libraries. If you don't acknowledge the "class pattern" for object inheritance then you are dismissing an incredibly popular use of OO.

Whether or not code reuse via OO is a good thing or not is a whole other debate though. I don't try to warp every problem into a class hierarchy, but sometimes it's a useful conceptual tool.

I really like Mozilla's docs. I read this one recently actually.