text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
|---|---|---|
And this render method goes ahead
and just renders a blank div | 3,962.79 | 3.33 |
with a blank UL. | 3,966.12 | 1.285 |
Yeah? | 3,967.405 | 0.499 |
AUDIENCE: In the previous
version of render, | 3,967.904 | 1.868 |
why was it returning a [INAUDIBLE]? | 3,969.772 | 3.597 |
JORDAN HAYASHI: Oh. | 3,973.369 | 0.791 |
So the question was in my
example to do app three, | 3,974.16 | 7.71 |
why was render up here returning false? | 3,981.87 | 4.23 |
So we'll talk about handling
events in a little bit. | 3,986.1 | 4.24 |
But basically, browsers actually
all have a way to handle events. | 3,990.34 | 4.49 |
And so if you do something
like click a Submit button, | 3,994.83 | 2.49 |
it will automatically go ahead
and submit a form for you | 3,997.32 | 3.57 |
and refresh the page. | 4,000.89 | 1.78 |
And so a lot of times, when we actually
want to handle that all in JavaScript, | 4,002.67 | 3.8 |
we have to have a way to disable
the automatic page refresh. | 4,006.47 | 3.394 |
And so there are a couple
different ways to do that. | 4,009.864 | 2.166 |
You can do something like event
dot stop propagation or event dot-- | 4,012.03 | 3.285 |
I forget the exact method
name, but it's something | 4,018.637 | 2.083 |
like stop this event from happening. | 4,020.72 | 1.71 |
Prevent default. Event
dot prevent default. | 4,022.43 | 2.36 |
And a shorthand for doing
both of those is just | 4,024.79 | 2.02 |
returning false out of
whatever handler they do. | 4,026.81 | 2.94 |
And so when I do return
false from this render, that | 4,029.75 | 3.687 |
means if I ever want
to do something, like I | 4,033.437 | 1.833 |
add to do, and hook it up to a button
that might automatically submit a form, | 4,035.27 | 4.77 |
I can return false from that
instead and automatically | 4,040.04 | 3.3 |
prevent that from happening. | 4,043.34 | 1.69 |
And so this is just some shorthand
for rather than having submit buttons | 4,045.03 | 5.15 |
automatically refresh a
page, it just blocks that | 4,050.18 | 3.21 |
and lets me handle it all in JavaScript. | 4,053.39 | 2.132 |
Cool. | 4,061.295 | 0.5 |
So back to this example in React. | 4,061.795 | 3.775 |
So we're up to this point where
we have a class called app. | 4,065.57 | 3.66 |
Right now, we have no state associated
with it, and all we're doing | 4,069.23 | 3.15 |
is rendering this empty list. | 4,072.38 | 1.84 |
And so how might we go about
implementing these features | 4,074.22 | 2.9 |
that we have in our to do project? | 4,077.12 | 3.141 |
Well, first, we're going to
want to start tracking something | 4,080.261 | 2.499 |
in [? our ?] state, right? | 4,082.76 | 1.083 |
Maybe we want to track the to dos. | 4,083.843 | 3.697 |
And so how do we go ahead and
create something called state? | 4,087.54 | 3.7 |
Well, first, we want to
invoke the constructor, which | 4,091.24 | 3.61 |
for now takes no arguments, since we're
not actually passing any props to app. | 4,094.85 | 4.83 |
First thing we do in the
constructor is always | 4,099.68 | 2.07 |
called the super, which is invoking
the constructor on React.Component, | 4,101.75 | 6.09 |
which gives us things
like this dot set state. | 4,107.84 | 2.519 |
And then now we have the
opportunity to initialize our state, | 4,110.359 | 3.271 |
so we can go ahead and do
this.state equals whatever. | 4,113.63 | 5.16 |
And so what might we
want to store in state? | 4,118.79 | 2.071 |
AUDIENCE: To do list. | 4,120.861 | 1.398 |
JORDAN HAYASHI: Yeah, the to do list. | 4,122.259 | 1.541 |
Is there anything else
that we should store? | 4,123.8 | 1.833 |
Nothing I can think of
off the top of the head. | 4,127.87 | 2.581 |
But thankfully, if we want to add
something later, it's very easy to do. | 4,130.451 | 2.999 |
And so let's just do to dos, and
let's store this all on an empty list. | 4,133.45 | 6.9 |
Cool. | 4,140.35 | 0.5 |
So now we have this concept of state. | 4,140.85 | 2.41 |
We now have this concept of to
dos, which is stored in our state, | 4,143.26 | 3.059 |
but we're not doing anything with it. | 4,146.319 | 1.87 |
And so let's actually render
those to dos to the screen. | 4,148.189 | 3.321 |
So we might want to do it
within the unordered list. | 4,151.51 | 3.36 |
Let's have something like
this dot state dot to dos. | 4,154.87 | 3.42 |
And again, we wrap things
in single curly braces | 4,158.29 | 3.189 |
when we want to execute
them as JavaScript. | 4,161.479 | 2.5 |
And so we have this dot state dot
to dos, which is an empty array. | 4,163.979 | 3.791 |
But we can't just take for granted
that it's always an empty array. | 4,167.77 | 3.36 |
The point of writing declarative code
is that we want this to hold true, | 4,171.13 | 4.14 |
no matter what the state is. | 4,175.27 | 2.07 |
And so we just assume that this is
full of to dos, and so we can go ahead | 4,177.34 | 3.479 |
and map over that and render each to do. | 4,180.819 | 2.011 |
So for each to do, let's
actually create a to do. | 4,186.52 | 2.85 |
All right, so I'm mapping out
the to dos, and for each to do, | 4,198.18 | 3.24 |
I'm creating this tag
called uppercase to do. | 4,201.42 | 4.29 |
So who remembers what
uppercase tags mean? | 4,205.71 | 5.26 |
AUDIENCE: It's a React component. | 4,210.97 | 1.79 |
JORDAN HAYASHI: Yeah,
it's a React component. | 4,212.76 | 2.79 |
And we now have to describe something
called a React component called capital | 4,215.55 | 4.14 |
to do. | 4,219.69 | 0.69 |
And so let's go ahead and do that. | 4,220.38 | 1.416 |
And so just like the examples
that I showed you earlier, | 4,224.1 | 2.72 |
where we abstracted out the
concept of creating a to do, | 4,226.82 | 2.357 |
we can do that in React as well. | 4,229.177 | 1.333 |
So let's have this thing called a to do. | 4,230.51 | 2.36 |
And what it does is it takes some props. | 4,232.87 | 2.83 |
We can call this variable
whatever we want, | 4,235.7 | 2.19 |
but the React convention
is to call it props. | 4,237.89 | 2.057 |
And what are we going to return? | 4,239.947 | 1.333 |
Well, let's just return an
unordered list, or a list item. | 4,241.28 | 4.89 |
What might we have in that list item? | 4,246.17 | 1.56 |
Well, we had an input of type checkbox. | 4,250.36 | 3.16 |
We had a button that
allowed us to delete. | 4,256.96 | 3.72 |
And last but not least,
we had some text. | 4,263.44 | 3.165 |
And what was in that text? | 4,266.605 | 1.605 |
Well, probably just props, dots-- | 4,268.21 | 2.46 |
we can call it the text for the to do. | 4,270.67 | 2.37 |
Cool. | 4,278.581 | 0.499 |
So now we declaratively just said,
hey, every time we want a to do, | 4,279.08 | 4.006 |
this is what it looks like. | 4,283.086 | 1.124 |
It's a list item, and
inside it, we have an input. | 4,284.21 | 2.284 |
It's going to be a checkbox. | 4,286.494 | 1.166 |
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