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And this render method goes ahead and just renders a blank div
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with a blank UL.
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Yeah?
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AUDIENCE: In the previous version of render,
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why was it returning a [INAUDIBLE]?
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JORDAN HAYASHI: Oh.
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So the question was in my example to do app three,
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why was render up here returning false?
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So we'll talk about handling events in a little bit.
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But basically, browsers actually all have a way to handle events.
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And so if you do something like click a Submit button,
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it will automatically go ahead and submit a form for you
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and refresh the page.
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And so a lot of times, when we actually want to handle that all in JavaScript,
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we have to have a way to disable the automatic page refresh.
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And so there are a couple different ways to do that.
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You can do something like event dot stop propagation or event dot--
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I forget the exact method name, but it's something
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like stop this event from happening.
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Prevent default. Event dot prevent default.
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And a shorthand for doing both of those is just
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returning false out of whatever handler they do.
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And so when I do return false from this render, that
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means if I ever want to do something, like I
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add to do, and hook it up to a button that might automatically submit a form,
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I can return false from that instead and automatically
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prevent that from happening.
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And so this is just some shorthand for rather than having submit buttons
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automatically refresh a page, it just blocks that
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and lets me handle it all in JavaScript.
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Cool.
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So back to this example in React.
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So we're up to this point where we have a class called app.
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Right now, we have no state associated with it, and all we're doing
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is rendering this empty list.
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And so how might we go about implementing these features
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that we have in our to do project?
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Well, first, we're going to want to start tracking something
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in [? our ?] state, right?
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Maybe we want to track the to dos.
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And so how do we go ahead and create something called state?
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Well, first, we want to invoke the constructor, which
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for now takes no arguments, since we're not actually passing any props to app.
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First thing we do in the constructor is always
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called the super, which is invoking the constructor on React.Component,
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which gives us things like this dot set state.
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And then now we have the opportunity to initialize our state,
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so we can go ahead and do this.state equals whatever.
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And so what might we want to store in state?
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AUDIENCE: To do list.
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JORDAN HAYASHI: Yeah, the to do list.
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Is there anything else that we should store?
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Nothing I can think of off the top of the head.
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But thankfully, if we want to add something later, it's very easy to do.
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And so let's just do to dos, and let's store this all on an empty list.
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Cool.
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So now we have this concept of state.
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We now have this concept of to dos, which is stored in our state,
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but we're not doing anything with it.
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And so let's actually render those to dos to the screen.
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So we might want to do it within the unordered list.
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Let's have something like this dot state dot to dos.
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And again, we wrap things in single curly braces
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when we want to execute them as JavaScript.
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And so we have this dot state dot to dos, which is an empty array.
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But we can't just take for granted that it's always an empty array.
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The point of writing declarative code is that we want this to hold true,
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no matter what the state is.
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And so we just assume that this is full of to dos, and so we can go ahead
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and map over that and render each to do.
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So for each to do, let's actually create a to do.
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All right, so I'm mapping out the to dos, and for each to do,
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I'm creating this tag called uppercase to do.
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So who remembers what uppercase tags mean?
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AUDIENCE: It's a React component.
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JORDAN HAYASHI: Yeah, it's a React component.
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And we now have to describe something called a React component called capital
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to do.
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And so let's go ahead and do that.
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And so just like the examples that I showed you earlier,
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where we abstracted out the concept of creating a to do,
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we can do that in React as well.
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So let's have this thing called a to do.
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And what it does is it takes some props.
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We can call this variable whatever we want,
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but the React convention is to call it props.
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And what are we going to return?
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Well, let's just return an unordered list, or a list item.
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What might we have in that list item?
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Well, we had an input of type checkbox.
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We had a button that allowed us to delete.
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And last but not least, we had some text.
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And what was in that text?
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Well, probably just props, dots--
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we can call it the text for the to do.
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Cool.
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So now we declaratively just said, hey, every time we want a to do,
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this is what it looks like.
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It's a list item, and inside it, we have an input.
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It's going to be a checkbox.
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