text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
|---|---|---|
oops, we should return this-- | 3,775.59 | 3.68 |
when you toggle that counter we
never actually tell this component, | 3,779.27 | 6.18 |
hey, stop incrementing. | 3,785.45 | 3.372 |
It's actually going
to keep incrementing. | 3,788.822 | 1.708 |
And so we can show that if
we have here, if we console | 3,790.53 | 2.94 |
that log we see that it's
incrementing, and if we toggle it, | 3,793.47 | 10.66 |
it's still logging. | 3,804.13 | 1.47 |
So counters now gone. | 3,805.6 | 2.29 |
So there's no counter here, it's
gone but it keeps saying increment. | 3,807.89 | 6.32 |
And, if we show it again, now look
at how fast it's incrementing. | 3,814.21 | 10.15 |
It's two every second because
the first counter created | 3,824.36 | 5.17 |
an incrementing function every 1,000
milliseconds and the second time | 3,829.53 | 4.2 |
we created one it also did. | 3,833.73 | 2.94 |
And so what if we did this again. | 3,836.67 | 1.59 |
Toggle and then toggle again. | 3,838.26 | 3.42 |
Now it's going up three every second. | 3,841.68 | 1.9 |
And if we did this a bunch of times,
you see it's going pretty crazy now. | 3,843.58 | 4.67 |
It's like five every second. | 3,848.25 | 2.072 |
And so that's not good. | 3,850.322 | 0.958 |
That's definitely not good at all. | 3,851.28 | 1.99 |
Say you had a super complex app
and hundreds of timers getting set | 3,853.27 | 4.55 |
and you kept toggling them. | 3,857.82 | 1.53 |
Eventually you're going to have a
big problem where a bunch of things | 3,859.35 | 3.03 |
are getting called and nothing
should be getting called. | 3,862.38 | 2.91 |
And so that's like a memory leak and
it could cause your app to crash. | 3,865.29 | 4.35 |
And so how might we
go about solving this? | 3,869.64 | 3.61 |
So, as we alluded to, there's
this thing called an unmount cycle | 3,873.25 | 3.11 |
where we have a chance to clean up. | 3,876.36 | 2.01 |
We can get rid of any
timers that we've created. | 3,878.37 | 5.16 |
And so you can actually do that here. | 3,883.53 | 3 |
And so, rather than just
setting the interval, | 3,886.53 | 2.22 |
we should actually track that
function that we created. | 3,888.75 | 3.06 |
And so you can do something like
this.Interval equals setInterval. | 3,891.81 | 6.18 |
And so setInterval actually returns like
an ID of the interval that you created. | 3,897.99 | 5.63 |
And so now we're tracking exactly
the interval that we created. | 3,903.62 | 4.94 |
And we can go ahead and right
before this component dies, | 3,908.56 | 4.07 |
so component will unmount, we
should actually clean that up. | 3,912.63 | 6.84 |
We can actually do clearInterval
and we pass in that ID. | 3,919.47 | 5.445 |
And so now you can see-- | 3,929.36 | 5.07 |
oops, things did not get updated. | 3,934.43 | 3.375 |
Let's actually copy all
this and refresh the page. | 3,937.805 | 7.617 |
And so when this loads,
you'll see that it will still | 3,952.06 | 4.5 |
log when it's getting shown. | 3,956.56 | 3.49 |
And so as this number is incrementing we
can see it saying, oh I'm incrementing. | 3,960.05 | 5.42 |
But when we toggle it that
number no longer goes up. | 3,965.47 | 7.41 |
And then, if we toggle it again,
it's going to continue incrementing. | 3,972.88 | 4.33 |
And, if we cancel that,
that incrementing function | 3,977.21 | 3.74 |
is no longer getting called. | 3,980.95 | 1.76 |
And that's because, over here,
when the component was created, | 3,982.71 | 5.3 |
so when the component mounts, we set
the interval for this button increment | 3,988.01 | 5.2 |
to happen every 1,000 seconds. | 3,993.21 | 2.75 |
But then later when we are no
longer returning that counter so | 3,995.96 | 8.72 |
the instance gets unmounted. | 4,004.68 | 1.5 |
It's no longer part of the React tree. | 4,006.18 | 1.67 |
Before it gets unmounted, we say
clear that interval and it clears. | 4,013.89 | 7.21 |
And then when it remounts
it creates a new interval. | 4,021.1 | 3.38 |
And when it gets unmounted again it
goes ahead and clears that interval. | 4,024.48 | 4.47 |
And so now we no longer
have any memory leaks. | 4,028.95 | 1.98 |
So does that whole lifecycle
process make sense to people? | 4,034.76 | 3.59 |
Do you have any questions
about these methods | 4,038.35 | 2.94 |
or why we might want to use them? | 4,041.29 | 5.78 |
Cool. | 4,047.07 | 0.5 |
Let's take a quick five
minute break and then | 4,047.57 | 2.36 |
after this, we'll go ahead and
start writing some React Native. | 4,049.93 | 2.88 |
Hello and welcome back. | 4,052.81 | 1.38 |
So if you are following Snack some
people had some questions about style | 4,054.19 | 5.16 |
and whether or not people
in industry chose to bundle | 4,059.35 | 2.79 |
this style with each component. | 4,062.14 | 2.46 |
And what I tend to
see mostly in industry | 4,064.6 | 2.67 |
is that people do indeed tend to
include the styles with each component | 4,067.27 | 4.5 |
because part of React's
component mindset | 4,071.77 | 2.64 |
is that each component
should be a standalone thing | 4,074.41 | 2.55 |
and it should include with it any event
handlers or JavaScript and any style | 4,076.96 | 5.25 |
as well. | 4,082.21 | 1.25 |
But there are many compelling
reasons to actually remove | 4,083.46 | 3.25 |
the style outside of that component. | 4,086.71 | 1.95 |
And one big compelling reason would
be something like color themes. | 4,088.66 | 3.51 |
So say you had some color theme where
you really liked crimson in your app | 4,092.17 | 5.91 |
and everywhere you were using crimson. | 4,098.08 | 2.37 |
And then say suddenly you wanted
to use something like blue. | 4,100.45 | 5.4 |
If you had everything
hard coded to crimson | 4,105.85 | 2.339 |
it might be a bit of a pain to go
through and find every instance | 4,108.189 | 3.21 |
of that crimson and change it to blue. | 4,111.399 | 1.991 |
But say you actually abstracted
out some value like primary color | 4,113.39 | 5.299 |
and instead used that in
all of your components. | 4,118.689 | 2.669 |
Then if you wanted to change the
primary color from crimson to blue | 4,121.358 | 2.791 |
it would be very easy. | 4,124.149 | 0.916 |
You would just do it in
one file and be done. | 4,125.065 | 2.265 |
So there are definitely compelling
reasons to remove the styles out | 4,127.33 | 3.87 |
of a particular component. | 4,131.2 | 2.61 |
And since React Native uses
JavaScript's objects to style components | 4,133.81 | 4.169 |
it allows you to do stuff like
create variables and import them in. | 4,137.979 | 4.541 |
And so are there reasons
to take the style sheets | 4,142.52 | 2.75 |
outside of any particular component. | 4,145.27 | 2.549 |
But generally if you
have a choice it's easier | 4,147.819 | 2.101 |
to just leave it in there
for organization sake. | 4,149.92 | 4.05 |
Cool. | 4,153.97 | 1.36 |
And so up until now we've been writing
a lot of React Native in this browser | 4,155.33 | 6.59 |
environment. | 4,161.92 | 0.78 |
And so let's actually figure out
and talk about how we actually | 4,162.7 | 3.6 |
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