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So now we have a way of recognizing which to do is which.
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3.23
And so say we wanted to get rid of one, it's now pretty easy to do that, right?
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6.3
So if we want to now remove to do, that should now do what?
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11.92
Does it make sense to have a remove to do with no arguments?
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4.341
Not really, right?
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0.749
Because we need to know exactly which to do we want to delete.
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It makes sense that we want to add a to do with no arguments,
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because there's no particular to do that we want to add.
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We create that text later.
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1.959
But when we want to remove a to do, we need
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to know exactly which to do to remove.
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1.75
And so now we should have remove to do actually taking argument.
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4.741
And so what argument should it take?
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Well, we created some sort of unique identifier field,
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3.02
so we can just take the ID.
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3.32
And so now how are we going to remove the to do?
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3.78
Well, we could do this.setState, which is the only way to update the state.
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5.8
And the to dos are what?
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3.87
They can take the old state's to dos and just filter them, where for each
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to do, what do we want to keep?
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5.71
Well, as long as the to do dot ID is not equal to the ID that we pass in,
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those are the to dos that we want to take.
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2.81
Great.
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0.96
But the Delete button is not working.
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3.87
Why not?
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1.17
Well, our component called to do is not doing anything
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6.18
when you click on the button.
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4.03
So how might we handle that?
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1.4
Well, that's where props come in.
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Since we can pass any JavaScript value as props,
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what's to stop us from just passing a function down?
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2.85
And so when we map over the to dos like this,
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we can actually also pass a function down.
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8.656
So we could pass something called onDelete and just pass a function.
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6.31
And what would that function do?
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Well, it's going to call this.delete removeTodo.
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4.68
And what are we going to pass in when we invoke that?
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2.962
Well, this todo.id.
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0.808
Does that make sense?
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0.874
So we're mapping over to dos, and for each to do in that array,
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we're going to invoke that to do function, that component.
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4.89
And what are we passing as props?
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1.8
We're passing it this thing called onDelete
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2.67
which is a function that invokes remove to do with that to do's ID.
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4.19
So for each to do that we create, we're passing
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a unique function that removes that particular to dos
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4.07
from our global state.
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And of course, we're also passing down the to dos,
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so it knows exactly which text to render.
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4.73
And so how do we get that to fire when we click the delete button?
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3.994
Well, that function's just a prop, right?
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3.03
So when we click that button, what should we do?
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4.02
Well, we should invoke props dot on delete.
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2.67
And so now when we add things, if we click that button,
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the correct one is deleted.
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3.12
Again, how does it know that that first one is the one that should be deleted?
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4.11
Well, it's because each to do that gets rendered,
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2.28
so when we map over the to dos in our state, we pass a unique on delete
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4.17
handler down.
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2.1
It's a function that gets bound to that particular to do's ID field.
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5.14
And so when we click that particular to do's delete button,
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3.68
it invokes remove to do with that ID, and so it knows
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2.52
to filter based on that particular ID.
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5.408
Does that make sense to people?
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Great.
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0.499
So we've handled the two big parts--
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well, the add and the delete part of the assignment.
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3.34
And so what are we missing?
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1.34
We're missing some way of tracking how many to dos we have total
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and how many to dos that we still have to complete-- or in other words,
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to dos that are unchecked.
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2.91
And so now we have a choice-- how are we going to handle this?
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Well, if we were back in Vanilla JavaScript world,
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a way to do that would just be to keep track
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of however many unchecked there are, keep track of however many total
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there are.
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0.99
And just mess with those values every single time we add, delete, or check
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5.22
or uncheck a to do.
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2.41
But in React land, that seems a little imperative for our like,
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3.18
and so there might be a more declarative way to do this.
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But in order to do that, we also need to track every single to do,
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whether it's checked or not.
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1.9
And so currently our to dos are an ID field and a text field.
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But maybe it would be better to also add a field of whether it's checked or not.
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3.63
And so now when we add to dos, we add an object with three keys--
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3.18
an ID which is guaranteed to be unique, because we're incrementing
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this ID counter, which lives outside of our app; the texts that we prompt for;
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and lastly, a value called checked, which keeps track of whether that to do
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is checked or not.
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2.04
And we should just initialize it with false,
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1.95
because there's no point in creating a to do.
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2.102
That's already done.
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3.569
Cool.
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0.499
And so now we're still missing one thing.
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So when we create to dos, we just create an empty checkbox.
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And so no matter what, it's going to be unchecked.
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2.52
And so we should set that check field to equal whether that particular to do
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is checked or not.
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0.83
And so how might we do that?
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1.29
Well, with props.todo.checked.
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1.62