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‫Let's continue building our application

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‫by creating a brand new component

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‫and by taking a first look at reusability.

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‫But first, let's get the starter files for this project

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‫from the files that we downloaded from GitHub.

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‫So right here in the starter folder,

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‫take these three, copy and then go into your project folder

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‫and I will copy them for now here into the public folder.

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‫So we have this folder of pizza images,

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‫we have this starter data and this index.CSS

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‫which we should probably move into this source folder.

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‫So make sure that you have these two files here

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‫after including the starter files.

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‫And now let's come back here

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‫and let's create that brand new component

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‫that I was talking about.

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‫So in React we write new components using functions.

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‫So function, and I'm calling this one pizza

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‫because it will contain some data about a pizza

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‫and then here for now

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‫we have no parameters to this function

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‫and then the function body.

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‫Now in React, there are two important rules

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‫when we write components as functions.

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‫First, the function name needs to start

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‫with an uppercase letter like this

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‫and second, the function needs to return some markup.

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‫So usually in the form of JSX,

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‫but we can't even return nothing, like returning null.

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‫But here, let's just return some H2 element, for example

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‫and then let's just write pizza.

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‫So give it a save, but of course nothing will appear here

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‫in the user interface, and that's

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‫because we're not including this new component anywhere

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‫and even ESLint is warning us about that here.

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‫So this yellow line which says pizza is defined,

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‫but never used.

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‫So again, we're not including this pizza component

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‫into our app component which is the component

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‫that is currently being rendered on the screen.

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‫So we can use our component here just like this.

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‫So pizza

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‫and then we immediately close the element like this.

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‫This however will give us an error.

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‫So right here, which we already saw before

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‫and the reason for this error

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‫is that each component can only return exactly one element,

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‫not two elements as we have here.

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‫So let's wrap this here into a div

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‫and sometimes it can become a bit annoying

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‫that VS Code automatically closes these elements for us,

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‫but anyway, now we get our pizza in the UI.

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‫And so that's because we now nested this pizza component

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‫inside this app component.

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‫And with nesting, I mean that we basically used

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‫or caught this component here inside app.

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‫What's very, very important to notice

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‫is that by nesting, we do not mean

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‫that we write a function inside this other function.

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‫So what we should never do

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‫is to nest the component declaration itself.

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‫So like this, this still works actually,

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‫but it's a very, very bad idea

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‫for reasons that we will learn about later.

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‫So never nest the function declarations,

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‫but always declare all your components in the top level.

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‫So just like this.

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‫So again, when we say nesting components,

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‫what we mean is that we call,

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‫so we include one component into another like this.

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‫Now, okay, so let's now make this pizza component here

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‫just a little bit more interesting

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‫and for that we are going to use our starter data here.

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‫So let's open up data.js

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‫and all we need is for is to select everything, then copy it

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‫and then let's just paste it here.

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‫Okay.

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‫So as you see right now we are doing all the development

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‫of this application in one big file.

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‫While in the real world we divide our code into modules

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‫and then include these modules into one another,

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‫but here I just want to keep it simple

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‫so we're not going to do that yet.

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‫So actually we can then delete this data.js

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‫and close this down.

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‫So for now, we will simply use this here as an example.

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‫So I will now copy, paste, let's say this pizza here

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‫and use that here as the name

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‫and then let's also grab the ingredients.

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‫So let's just copy and paste all of this text

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‫and notice that I'm really only interested in the text.

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‫We don't need, of course, these quotes

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‫because, again, this is just like writing HTML

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‫and there you also don't need quotes, right?

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‫So here, let's create a paragraph

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‫and then immediately you see we get this red underline here

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‫which is because, again,

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‫we are trying to return two elements here

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‫which is not allowed.

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‫Okay, so here what I like to do

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‫is to then move up this line here using a shortcut.

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‫So let's see what that is for you.

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‫So it's this move line up.

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‫So you should probably get used to this shortcut

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‫and this one so where we move lines up and down,

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‫so like this for example,

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‫so that's very, very helpful

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‫and we're gonna do that all the time.

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‫We just need to get rid of this semicolon that we have here,

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‫which was right there.

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‫Okay, so we have some text,

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‫now let's also actually use this image

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‫that we have in the public folder.

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‫So yeah, this one right here.

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‫So remember how I mentioned in the beginning

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‫that all the assets of the app

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‫will go into this public folder because Webpack,

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‫so the module bundler will then basically

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‫automatically get them from there.

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‫And so we can now write an image here.

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‫So again, just like HTML,

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‫and then if we write a path to the image like this,

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‫spinaci.jpg,

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‫then Webpack will automatically get that here

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‫from this folder and let's see if that works.

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‫And indeed, there goes our image.

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‫Now we get these yellow underline here

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‫and that's because an ESLint rule

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‫which says that images always should have an alt prop.

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‫So let's just add that here.

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‫So to make it a little bit more accessible,

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‫let's just put the name of the pizza here

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‫and then ESLint is happy.

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‫So we have this component here

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‫and now let's talk about the idea of reusing this component.

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‫And for now, all we're going to do to reuse this component

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‫is to basically use it several times.

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‫So let's do three times just so you can see

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‫that now this piece of UI, which is the pizza component,

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‫will be included three times.

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‫So three times this delicious spinach pizza.

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‫Nice. Now of course the data here in all of them

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‫is now the same because we didn't customize that data yet,

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‫but we will do that later of course,

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‫when we talk about props.

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‫For now,

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‫I just want you to get this really important concept

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‫that we can call each piece of the UI

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‫or in other words, each component multiple times here

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‫in order to reuse it

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‫and that's a fundamental concept

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‫of writing React applications.

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‫Now, just one final thing here,

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‫and this has nothing to do with code,

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‫is that maybe you have noticed

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‫that we get all these colored lines here in the sidebar

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‫and even down here.

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‫Now the reason for this is that when we create a new project

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‫with Create-React-App,

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‫it will actually automatically set up this project

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‫as a GitHub repo.

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‫That's why you also get all these different colors here

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‫and also here you see all the changes that we have made

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‫to the different files.

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‫So here we deleted some stuff, we modified some stuff,

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‫and here these images are still untracked.

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‫Now, since we're not really going to use GitHub

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‫as we build these small projects,

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‫I actually just want to remove these colored lines here

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‫from the gutter, so from this place,

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‫and for that we can go to our settings

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‫and then just search for diff decorations.

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‫So here the default is all, so let's set it to none.

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‫And so then our editor will look

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‫just a little bit cleaner here,

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‫and we can close down the sidebar

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‫and with this, we finish this lecture

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‫and are ready to move on.