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And what are we going to do?
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Well, we should attach to the instance the array.
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And that's basically saying, when I'm constructed,
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I expect to have one argument, which is just an array.
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And the only thing I'm going to do when creating this set object
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is just store a reference to that array.
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By doing this.arr = arr.
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And so in this case, the this keyword is referring
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to the instance of the object.
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Cool, so let's try adding a couple of different methods to this.
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So we should be able to support add, which should take a value.
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We should be able to support delete, which also takes a value.
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And we should have something called has, which checks for inclusion.
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So how might we do something?
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How might we add to this class?
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Does anybody have any ideas?
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AUDIENCE: [INAUDIBLE]
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JORDAN HAYASHI: Exactly.
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So we should use something like push to add to the array.
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But before we do that, we should make sure that that number does not already
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exist.
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And so maybe we should implement the has method first, which is a great idea.
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Let's go ahead and do that.
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So how might we do has?
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Well, it turns out on the array prototype,
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we already have something called includes, which tells us
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if an array includes a value, so we can just do that.
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We can do return this.arr.includes(val).
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And so now that we have that, how might we take care of add?
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We should say, oh, well, if this does not have the value already, add to it.
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And so here I use this.has.
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So this here is referring to the instance of the set,
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and so this.has is referring to this method
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down here, on this particular instance.
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And then when I do this.arr, this still refers to the instance of this set.
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And so we're just getting at this array property that we have,
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and we're pushing that value to that array.
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Cool.
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So how might we go about this delete?
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AUDIENCE: [INAUDIBLE] has value.
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JORDAN HAYASHI: Yeah, we can check if we have the value,
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but it doesn't really matter all that much.
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A quick and easy way would just be doing this.arr = this.arr.filter
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and then we can just filter by the values.
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So we could say, oh, we want for every x in here,
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we want the x's that don't equal this value.
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Cool.
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And so we can go ahead and run this to see if it works.
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Oops.
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While I edit, I should flip these.
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And we go ahead.
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S should have five members and actually has-- ooh, we forgot to influence size,
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actually.
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And so we took care of all of the methods,
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but we didn't include the size.
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And so we should be able to return the size of this set.
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How might we do that?
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Well, this is interesting.
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So we should be able to get at this value by doing the instance.size.
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And JavaScript actually has a convenient way.
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We can do get size, which is saying, when
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somebody tries to get at the value or the property.size,
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actually run this function.
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So this is just syntax for that shortcut.
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So how might we implement size?
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AUDIENCE: [INAUDIBLE]
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JORDAN HAYASHI: Yeah, just return this.arr.length.
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So now we can run this, and we see I should have five members,
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and it actually has five.
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So that's good.
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S should contain 5.
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That's true.
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That works.
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S should contain six.
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It's true.
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S should have six members, and actually has six, so we're good still.
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S should no longer contain six.
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That also returns true.
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And lastly, S should have five members, and actually does indeed have five.
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So does anybody have any questions with our implementation of set as a class?
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Great.
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So it turns out JavaScript actually already has a set class,
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and it works exactly as we implemented.
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But say we actually wanted to use the native implementation of set
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and actually add some stuff to it.
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So that's where we use these other keywords, called extends and super.
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So extends is the JavaScript way of saying,
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hey, I want to start with a base class and actually add to it.
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Extend this class.
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And super, as we'll see in a second, is when we're writing that class,
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so we can refer to the original class using this keyword.
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And so in this example called my set, we're
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going ahead and extending that set with a bunch of different things.
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And so here you see constructor.
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It still takes an array.
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And the first thing that we do is we invoke super on that array.
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So this is basically saying, hey, we're extending a set.
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So when you do the constructor, the first thing you should do
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is actually run the original set's constructor.
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And then let's also keep track of this.originalarray
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