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In the last talk-through, we learned how [br]to make an object type

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to represent our two Winston-like objects

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and then initialize them [br]with the constructors.

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Now, an object type doesn't just [br]have to be associated with properties.

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It can also be associated [br]with functionality.

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Think about the world and all [br]the object types in it, like us humans.

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We all have height and age,

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but we also have things we can do like [br]sleep, and eat, and program.

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And we wanna be able to associate [br]those functions with those object types.

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In this program, which is just where [br]we left off from last time,

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we've a funciton here, drawWinston,[br]that we call on both Winston objects.

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Wouldn't it be neat if we could just [br]attach that to the Winston object type?

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Well we can, and it's easy to do.

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So underneath our constructor, [br]we're gonna write Winston --

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capital W -- dot prototype.

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And the "prototype", that's a new word [br]that you probably haven't seen before.

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And the prototype is this property [br]of an object that we can attach

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functions to and it will mean that every[br]object that's an instance of that

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will then have those functions on them.

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So we can say dot prototype and then dot, [br]and then the function name.

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So we say draw, equals, and then we can[br]go and take our drawWinston code

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and we can just put it, [br]move it, inside here.

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All right, so now what we've done here [br]is we've attached a draw function

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to our Winston prototype.

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And that means that we should be able[br]to call draw() on any Winston-type object.

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All right, so we should be able to call [br]draw() on winstonTeen or winstonAdult.

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And when we have a function like this, [br]that we can call on an object,

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we actually call that a "method." [br]So you might hear me say "method" now.

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So let's say this is "the draw method." Okay.

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So now we'll delete this, and we'll delete this,[br]and now we're gonna see, can we call draw()?

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winstonTeen.draw()

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Okay. We have an error.

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We've had this error sticking out here, [br]so it says "winstObject is not defined"

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Okay. So, before, we were passing [br]this argument into drawWinston,

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which was the Winston object, [br]but now we're not passing it any more.

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So, we could change this to pass it,[br]and then, let's see,

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what would we pass here?[br]We'd have to pass winstonTeen.

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Okay, that worked, but that seems [br]also really silly.

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I'm already calling draw [br]on the object itself.

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I shouldn't have to pass in[br]the object as well.

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That seems redundant.

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And that's true, [br]we shouldn't have to do that,

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So let's delete this here, [br]and now let's think.

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If we're inside the object, [br]what could we use

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to access the properties of the object?

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Well, you might look up at our constructor[br]and remember that special keyword

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"this" and think "Ahh, what if we just[br]change this, to this!" (laughter)

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So we change winstObject to "this".

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Because we're inside the object right now.[br]This function is being evaluated

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on the object, so the "this" [br]will refer to that current object.

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And so that way we can just say "this" [br]and we'll get access to all

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the properties of this current object.

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And that totally works, see? [br]Isn't that cool?

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So now we can then say winstonAdult.draw()

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Tada! And it will access [br]the properties of winstonAdult

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because that's the object [br]it's being called on.

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So that's what's really cool about [br]this "this" keyword,

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even though it can be kinda [br]confusing to say sometimes.

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All right, so, that was a lot of fun. [br]So let's add another method.

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Okay, so, what else might Winston do?

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Maybe he'll talk. So we'll make a [br]Winston.prototype.talk

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so we can attach as many methods [br]as we want to the prototype.

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So we'll say, "I'm Winston!"

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And then we'll just say this.x+20, [br]and this.y+150.

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And then, y'know, nothing happened,

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but of course that's because I didn't [br]actually call that function yet.

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So, let's make the teen talk, [br]winstonTeen.talk() [inaudible] talk all the time

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Okay. I'm Winston, tada! [br]And then winstonAdult.talk()

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Tada!

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All right, so now we have this Winston [br]object type that has properties:

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nickname, age, x, y; and it has[br]functionality: behaviors, methods;

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that act differently depending on[br]the properties,

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and we can create as many instances [br]of Winstons as we want

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and call any of these methods on it.

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It's pretty cool, huh?