text
stringlengths 1
81
| start
float64 0
10.1k
| duration
float64 0
24.9
|
|---|---|---|
is the array that's passed in. | 756.47 | 1.46 |
And so we'll use that later to
use this thing called reset. | 757.93 | 4.68 |
And so say we wanted to every single
time we added a value to this set, | 762.61 | 3.78 |
we also wanted to log, hey,
we added a value to this set. | 766.39 | 4.35 |
So we can just start writing
this method called add. | 770.74 | 3.29 |
It takes a value just
like any other example. | 774.03 | 2.114 |
But instead of implementing
add ourself, we're | 776.144 | 1.916 |
just going to use the native
implementation of add. | 778.06 | 2.25 |
And so that's where we use super.add. | 780.31 | 1.6 |
So super, again, refers to the
class that we're extending. | 781.91 | 4.57 |
And so when we invoke
super.add, it goes ahead | 786.48 | 2.35 |
and does that using the
native implementation. | 788.83 | 2.106 |
And then since we're going to extend
it with some additional logging. | 790.936 | 2.874 |
We're just going to log, hey,
we added this val to the set. | 793.81 | 3.09 |
And if you're not familiar with
this, if you use the backticks, | 796.9 | 3.48 |
you can go ahead and add
variables in line, in the string, | 800.38 | 2.85 |
and it'll go ahead and
substitute those in. | 803.23 | 3.28 |
And so you see we added a
couple of other methods here. | 806.51 | 2.36 |
We have to array, which is basically
saying, hey, I actually want the array, | 808.87 | 3.48 |
and not the set. | 812.35 | 0.7 |
And so we can just
return Array.from (this). | 813.05 | 2.41 |
We're passing in the entire instance. | 815.46 | 2.86 |
And lastly, we have a
reset, which is saying, hey, | 818.32 | 3.27 |
I want the original set
that I had, or at least | 821.59 | 4.71 |
a new set with equivalent value. | 826.3 | 3.06 |
So you can return a new my set. | 829.36 | 1.38 |
So notice you are referencing
my set inside that class. | 830.74 | 3.72 |
We want a new one, and
we're going to pass in, | 834.46 | 2.22 |
as the array here, the original array. | 836.68 | 2.12 |
So this is an example of us extending
a class that already exists. | 841.65 | 4.6 |
And as you see, if we want to
reference methods on that original, | 846.25 | 4.38 |
we just use that super keyword. | 850.63 | 3.48 |
So any questions on sets,
how we define them-- | 854.11 | 3.09 |
or sorry, classes and how we
define them, how we extend them? | 857.2 | 4.2 |
So why might this be useful? | 861.4 | 3.82 |
So as you guys are
doing on your project, | 865.22 | 3.5 |
you're keeping track of
these things called to dos. | 868.72 | 3.07 |
What if we actually
had a class for to do? | 871.79 | 3.59 |
And when you invoke this constructor
on some configuration object, | 875.38 | 4.419 |
what if it pulls out the text
and whether it's checked or not | 879.799 | 2.541 |
and stores it as part of
[? its ?] class instance? | 882.34 | 2.732 |
And say we want to
render it to the page. | 885.072 | 1.708 |
What if we could just
return some HTML like this? | 886.78 | 2.67 |
It would be quite handy, right? | 891.699 | 1.291 |
And that actually is
our next topic, react. | 892.99 | 5.46 |
So react is a JavaScript
library, and it allows | 898.45 | 2.52 |
us to write declarative views that will
react to changes in data automatically. | 900.97 | 4.716 |
It allows us to abstract complex
problems into smaller components, | 905.686 | 3.754 |
and it allows us to write simple
code that still perform it. | 909.44 | 3.29 |
And so I use this word in the
first bullet, declarative. | 912.73 | 2.91 |
So what the heck does that mean? | 915.64 | 2.5 |
So in CS50, we learned a paradigm
of coding called imperative. | 918.14 | 5.93 |
And today we're going to talk
about declarative coding. | 924.07 | 3.15 |
So the difference in
imperative and declarative | 927.22 | 2.58 |
is like asking the difference
between how you do something | 929.8 | 3.33 |
and actually what you want out of it. | 933.13 | 3.21 |
So imperative programming
outlines a series of steps | 936.34 | 3.27 |
to get to what you want,
whereas declarative, | 939.61 | 2.94 |
you just say what you want. | 942.55 | 2.2 |
And it's just an implementation
detail on how to get it. | 944.75 | 4.07 |
And so we've learned a few different
languages through CS50 in this course. | 948.82 | 3.57 |
A couple that come to mind
are HTML and JavaScript. | 952.39 | 4.08 |
So in HTML, do we tell
the browser exactly how | 956.47 | 3.48 |
we want to render all of these things? | 959.95 | 3.24 |
Do we tell it exactly how we
want the DOM to be constructed? | 963.19 | 4.26 |
No, we just tell it what we want. | 967.45 | 2.61 |
And so HTML is considered a declarative
language, because you just say, | 970.06 | 3.9 |
hey, I want this. | 973.96 | 0.81 |
And browsers are in charge of
just giving you what you want. | 974.77 | 5.69 |
Rather, with JavaScript, as you'll
see in your first project, when | 980.46 | 2.95 |
you want to do anything to
the DOM with JavaScript, | 983.41 | 2.4 |
you tell it, oh, first
get me a new element. | 985.81 | 3.57 |
Call it a div. | 989.38 | 1.41 |
Then do this. | 990.79 | 1.5 |
Then maybe append it to the tree. | 992.29 | 1.65 |
Then maybe add a class to it. | 993.94 | 1.208 |
Maybe give it some inner HTML. | 995.148 | 2.362 |
And so you're telling it exactly
what you want and how to do it. | 997.51 | 2.75 |
And so that is the more
imperative way of programming. | 1,000.26 | 4.018 |
So let's take this into an example. | 1,007.35 | 1.9 |
Say we had a classical
guitar here, and say we | 1,009.25 | 2.95 |
wanted to actually create this guitar. | 1,012.2 | 3.75 |
So in an imperative way,
how would you describe that? | 1,015.95 | 3.43 |
Well, you would say, oh,
I need a head over here. | 1,019.38 | 3.41 |
I need to add some pegs to it. | 1,022.79 | 1.26 |
Maybe I want the neck. | 1,024.05 | 1.47 |
Maybe I add some frets to that. | 1,025.52 | 2.085 |
Oh, I need to create the body and attach
them all and then maybe return that. | 1,027.605 | 4.415 |
And what would be a more declarative
way of creating the guitar? | 1,032.02 | 3.16 |
You just say, I want a guitar. | 1,037.96 | 1.8 |
Maybe tune the strings to this. | 1,039.76 | 1.319 |
And so an example in pseudo
code would be like this. | 1,041.079 | 8.091 |
So say we have a guitar, and
say we have some function | 1,049.17 | 2.92 |
called create element, similar to
what we have in the document in HTML. | 1,052.09 | 5.86 |
And say we know exactly
what strings we want. | 1,057.95 | 2.3 |
How might we go about
creating this guitar? | 1,060.25 | 3.45 |
Well, first we might want to do
something like let's create a head. | 1,063.7 | 3.24 |
Again, telling whoever's
listening exactly what we want. | 1,073.15 | 4.7 |
And then maybe for 6 pegs, maybe we
want to start adding pegs to that head. | 1,077.85 | 11.63 |
And so now we, in a very terse
manner, have a head with six pegs. | 1,101.27 | 6.31 |