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We're going to have a button called delete.
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It doesn't actually do anything for now.
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And we also have a span, and what's that value of the span?
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Well, just look at my props and grab the text.
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OK, so now what do we have to do?
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Maybe we should add a way to add to dos.
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So let's create a method called add to do.
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And what should we do first?
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Maybe we should get some text.
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So there are many different ways to do this.
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Let's just for now prompt.
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And then what do we want to do with that?
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We have text.
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What should we actually do with it?
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AUDIENCE: Add it to the to do list.
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JORDAN HAYASHI: Yeah, we should add it to our to do list.
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And how are we going to do that?
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We can just do this dot state equals something, right?
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No.
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There's only one way to update state, right?
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We should do this dot set state.
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And what are we doing?
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Well, we have the to do equal this dot state dot to dos.
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And then additional thing.
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And so the way that we've added to an array
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thus far is by doing this sum array dot push.
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What that does is it actually mutates the array.
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And so the way that React knows that it should update
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is it sees if the values that are passed to it are different.
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And as we learned a couple lectures ago, all objects
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are actually stored by reference.
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And so when we go ahead and mutate an object,
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the reference doesn't actually change.
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And so the React paradigm is rather than mutating these props,
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we should actually create new ones.
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And so a quick way to create a new array is
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by using this dot dot dot notation, which
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means given an array, if you dot dot dot array,
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it just pulls out all of those values of the array.
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And so when we do something like brackets dot dot dot some array,
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it pulls out all the values of that array and puts it into a new array.
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And so this is a quick way of cloning an array.
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And so now the array reference is changed, but the values in there
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are all the same.
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And so now we've cloned the array, and now we should add a new to do.
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And so let's call our to dos objects that have a text field,
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and that can be the text.
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So there's a small bug in our program now.
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Well, one, we don't know how to add a list.
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Add to that.
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So let's go ahead and create a button that can add a to do.
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So now you have a button, but it's not actually
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doing anything when we click it.
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So first we need to set up an event handler,
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so when that button is clicked, what should it do?
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Well, it should do this dot add to do.
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So what is wrong with this code?
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Why isn't it working?
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Yeah, this is not bound to what it should be.
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And so how are we going to fix that?
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Well, the easiest way is to just declare an arrow
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function in line here, which will lexically bind what we want it to do.
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And so now we have another bug, so we declared
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to do to be a list item with an input, a button, and a span.
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And we see the input in the button, but we don't see any spans.
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So does anybody spot exactly why that's happening?
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So what text are we populating that span with?
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Props dot text.
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And so what does the object called props--
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what values are in there?
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They're key value pairs that are mapped to what are passed in here.
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Are we passing a key called text into to do?
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No, we're not.
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We're only passing something called to do, right?
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To do may have a value called text, but in order
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to actually access that, what we would have to do is to do props.todo.text.
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And that will allow us to pull up the correct field.
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So now we have a way to add to dos.
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Great.
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That doesn't make much of a to do app.
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We should be able to check and uncheck, which we can.
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But we're not really handling that in state.
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We have no way of telling whether these to dos are checked or not,
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and we also have no way to delete to dos.
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And so we need some sort of way to recognize which to do is which.
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What are some strategies to go about doing that?
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Can anybody think of one?
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AUDIENCE: [INAUDIBLE]
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JORDAN HAYASHI: Yeah, we should give each one an ID.
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That way, if we can guarantee that those IDs are unique,
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then we'll have a unique way of recognizing each to do.
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And so let's go ahead and do that real quick.
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So a very easy way to do that would be to do something like this--
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have some value called ID declared outside, initialized to 0.
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And every time you create a new one, you just increment that.
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And so now every single time we add a to do, it has an ID field.
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And we're guaranteed that it's unique, since it's
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a counter outside the state of our app.
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Does that makes sense?
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So how does that help us?
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