text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
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if I'm looking for
these functions, they're | 4,543.12 | 2.01 |
all going to be declared
together at the bottom. | 4,545.13 | 2.22 |
And they might be used everywhere,
but all the function declarations | 4,547.35 | 3.06 |
are all going to be here. | 4,550.41 | 1.041 |
So that might be a feature because
it's good for organization. | 4,551.451 | 4.209 |
So say we're to play devil's advocate. | 4,555.66 | 2.91 |
Who might see this as a bug? | 4,558.57 | 2.346 |
Uh huh. | 4,574.038 | 3.162 |
OK. | 4,577.2 | 0.5 |
So the question is, like, why
can we declare two variables | 4,577.7 | 2.872 |
with the same name when they look
like they're in the same scope, | 4,580.572 | 2.708 |
specifically with this var keyword? | 4,583.28 | 2.82 |
Which is another thing where it's a
bug/feature that a lot of people use. | 4,586.1 | 5.66 |
And so if JavaScript were to be updated
and that bug/feature were to disappear, | 4,591.76 | 4.99 |
a lot of code would break. | 4,596.75 | 2.52 |
So a lot of people have
took advantage of this. | 4,599.27 | 1.98 |
And basically it's the same thing as
like, why is typeof a null object? | 4,603.862 | 2.958 |
Just because it is. | 4,609.77 | 1.08 |
And we can't change that because
people rely on that behavior. | 4,610.85 | 4.39 |
I know it's kind of an anti-answer,
but does that kind of makes sense? | 4,615.24 | 3.86 |
Yeah, you should-- so there's not
really a good reason to use var anymore. | 4,622.34 | 4.99 |
With ES6, everything
supports const and let. | 4,627.33 | 3.97 |
And so I've been using them in all
of the examples except for these. | 4,631.3 | 5.065 |
And I think you should
definitely use them as well. | 4,636.365 | 2.125 |
The reason I'm getting var
is one, so if you see this, | 4,638.49 | 3.68 |
you know what's kind of going on, and
because a lot of legacy code-- a lot | 4,642.17 | 3.54 |
of code written two, five
years ago, 10 years ago | 4,645.71 | 3.18 |
uses var just because
it was the only option. | 4,648.89 | 1.92 |
One thing that I didn't mention
earlier is that you can also | 4,653.76 | 3.612 |
declare a variable like this. | 4,657.372 | 1.208 |
So this is another way
of declaring a variable. | 4,668.47 | 4.08 |
This creates a global variable. | 4,672.55 | 2.517 |
It's something that you probably
won't see that often, there's | 4,675.067 | 2.583 |
really no reason to do it. | 4,677.65 | 1.77 |
But in case you ever see
that, that's what it is. | 4,679.42 | 4.27 |
So if you declare a variable without
giving it a keyword like let, const, | 4,683.69 | 3.555 |
or var, it creates it globally. | 4,687.245 | 2.18 |
But there's no reason for
you to use this, really. | 4,692.23 | 3.21 |
It's just if you ever see
it, that's what it is. | 4,695.44 | 2.398 |
Any questions at all about scoping? | 4,701.19 | 2.38 |
It's a pretty important concept. | 4,703.57 | 3.95 |
And for online folks as well,
remember, you can post in Slack | 4,707.52 | 3.18 |
and the staff will either field
those questions or pass them to me. | 4,710.7 | 4.846 |
Cool So let's move on to
our final topic of the day. | 4,719.21 | 2.72 |
So the global object. | 4,726.37 | 2.11 |
So the way these things all work
is basically in any given runtime, | 4,728.48 | 7.46 |
there's this thing
called a global object. | 4,735.94 | 2.65 |
And so all variables, all
functions are actually | 4,738.59 | 2.63 |
keys or parameters or
methods on the global object. | 4,741.22 | 3.9 |
So in browser, there's
this thing called a window | 4,745.12 | 3.18 |
which is a global object of a window. | 4,748.3 | 1.75 |
So this is a browser environment. | 4,750.05 | 5.78 |
And if I type window, I see this thing. | 4,755.83 | 3.92 |
And it has a lot in it. | 4,759.75 | 4.13 |
But basically the window
is this global object, | 4,777.01 | 2.27 |
and on it there is all sorts of stuff. | 4,779.28 | 3.01 |
So we see $0, $0a. | 4,782.29 | 3.17 |
So these-- so any variable that
you declare in this console | 4,785.46 | 4.47 |
gets put onto this global
object called window. | 4,789.93 | 3.96 |
And so actually, let me open
a brand new browser tab. | 4,793.89 | 2.83 |
And we'll get a little
bit of a cleaner window. | 4,803.212 | 1.958 |
So the reason that we saw these
things called $0, $whatever, | 4,805.17 | 3.13 |
is because I open these dev tools on
the same tab as my lecture slides. | 4,808.3 | 7.03 |
And the way that Google
Slides works is since it's | 4,815.33 | 5.79 |
something dynamic on the web,
it has to be using JavaScript. | 4,821.12 | 3.09 |
And since it's using
JavaScript, obviously it's | 4,824.21 | 2.01 |
creating a bunch of functions,
it's creating a bunch of variables. | 4,826.22 | 2.75 |
And all of these things end
up on the window object. | 4,828.97 | 2.32 |
And so when we check out--
when we inspected the window | 4,831.29 | 2.7 |
object of that particular tab,
there was a bunch of stuff | 4,833.99 | 2.79 |
on it because that's how
Google Slides is working. | 4,836.78 | 3.72 |
And when we created a new
tab, this is a brand new tab | 4,840.5 | 6.66 |
and therefore no JavaScript
has been executed, | 4,847.16 | 2.08 |
so there's a lot fewer variables
and stuff on this new tab. | 4,849.24 | 5.7 |
And so whenever we
create new variables-- so | 4,854.94 | 2.09 |
say we do const x equals this is
a new variable, we see x is this. | 4,857.03 | 7.98 |
We can also do this window.x-- | 4,865.01 | 3.76 |
I declare it as a const. | 4,868.77 | 1.5 |
So the way that browser windows
handle these blocks of variables | 4,879.24 | 2.71 |
is a little bit different. | 4,881.95 | 1.91 |
So we'll use var for
the sake of explanation. | 4,883.86 | 2.92 |
So when I create this new
variable called var y, | 4,886.78 | 3.65 |
it is the exact same thing as window.y
And so if we inspect the window, | 4,890.43 | 9.03 |
we see a bunch of things that are part
of the JavaScript API, the browser | 4,899.46 | 3.38 |
API, all of these things. | 4,902.84 | 2.23 |
And if we go all the
way to the very bottom, | 4,905.07 | 7.03 |
so this is stuff that is
created in the new tab. | 4,912.1 | 5.258 |
L, M, N, O, P, Q, R,
S. We see this y here. | 4,917.358 | 5.162 |
So part of that window object
is that variable called y | 4,922.52 | 3.41 |
that we stuck on the window. | 4,925.93 | 1.55 |
And so even though we declared
it with var y equals something, | 4,927.48 | 3.31 |
it ended up on that
global object, and that's | 4,930.79 | 2.19 |
how JavaScript keeps track of
all of your valuables and stuff. | 4,932.98 | 4.98 |
And so what happens when we're in the
node environment and we type window? | 4,937.96 | 7.64 |
up window's not defined. | 4,945.6 | 1.692 |
And it's because in
the node environment, | 4,947.292 | 1.708 |
the global variable is not called
window, it's actually called global. | 4,949 | 3.13 |
And if we type global, we
now see all of these things. | 4,952.13 | 5 |
And a lot of this will overlap with
that window object in the browser, | 4,959.87 | 3.76 |
but since the browser API has
things in it that is not necessarily | 4,963.63 | 4 |
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