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OK it will come back.

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So this lesson is one that I'm pretty excited about making.

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I hope that you enjoy it.

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We're going to be writing our very first express app before we actually do that.

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I want to take 30 seconds.

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It'll be really short I promise.

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Just review two important topics how an existing app works so the dog app that I've already shown and

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then the basics of the HTP request response lifecycle.

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OK let's get started.

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I'm going to begin by talking about HTP requests and responses.

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So remember when I go to a u r l like Google dot com and I hit Enter I'm asking for a web page I send

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an HDTV request and that request has a particular verb or type.

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Is it a GET request or a POST request or some of the other ones we haven't really seen yet.

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And then I potentially send some data along with the request and the server that receives my request

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the server that I'm requesting Google has some code that decides what page to send me back.

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So it sends me that Google home page or maybe it sends me the Google logon page or the G-mail page or

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a page says My password is incorrect whatever it is.

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The server is deciding what to send back.

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And then it responds with a response.

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So I send a request server side code figures out what I'm asking for and then it does some stuff and

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then send feedback a response that is fundamentally what we're going to use Express to do.

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So I have this dog demo app that you may remember.

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It's very very forgettable.

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Just a simple app that has a database that we've connected to and a user can view all the dogs in the

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database.

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Each dog only has a name and a breed entirely useless.

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But it is nice and simple and I think it's a good illustration of how Express works.

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So we have some code in here.

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Things like requiring Express and requiring a database.

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But most importantly are these three chunks and these are called wraps and we'll be writing our own

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routes and just a few minutes routes or the code that are responsible for listening and receiving those

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requests that I talked about and then deciding what to send back.

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So in this case we have code that is listening for a request to the home page just to slash then we

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have some code that's listening for a get request to slash dogs and we have some other code that's listening

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for a post request on slash create dogs and then inside of the routes we're running some code.

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In this case we're just rendering the home page.

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So that's going to respond with the contents of our home page which is another file somewhere else in

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this one.

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When someone asks for slashed dogs as a get request we find all the dogs and then we render the dogs

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page and send all the data for the dogs.

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Along with that.

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And when someone creates a dog we're sending a post request to create dog.

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We're going to add a dog to the database and then redirect them back to the dog's page where they can

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view all the dogs.

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So don't get too intimidated by the syntax and all the different pieces will be introducing this one

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little bit at a time.

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But the very first thing that everything starts from is this idea of a route and routes are just bits

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of code that will run some other code depending on the request that is received on our server.

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So then that brings me to the next point which is starting our server.

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So we have to run the file which is called apt.

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Yes node apt.

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Yes just like that.

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And then it needs to go.

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In this case to port 3000 which will actually be different for us in cloud 9.

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But if I go to Port 3000 and I refresh I get the home page because I made a request to slash and there's

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some code that when I make a request to slash sends me the home page.

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Same thing if I go to slash dogs there is another bit of code that is listening for a request as a get

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request to slash dugs and it sends me all the dogs back.

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And then lastly I can make a new dog and hit submit and that sends a post request to slash create dog

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.

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And this code is wrong.

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All right.

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So that's all I wanted to review before we move on to writing our own code.

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The one big takeaway from all of that if you just totally slept through it the one big takeaway is routes

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routes are important.

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Rasner how we listen for particular requests and then run some other code depending on the requests

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that we get.

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OK so now it's the moment that you've been waiting for.

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Hopefully you've been waiting for this.

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We're going to go ahead and create our first express app so I'm going to go back to cloud nine and I'm

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going to make a new directory.

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I'm just going to call it first express app and CD into that and then I'm going to make a new file app

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yes and then we'll open that up and we'll start just constantly logging our express app.

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We'll go here and save and let's just run it.

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And all right we get our console log.

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So now what we need to do is install Express and if I go back to the Express docks you can see we just

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run NPM install express and I did mention in the last video that we were going to talk about dash dash

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save in this video and we are going to keep it until the very end.

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It doesn't make a difference at all in the functionality of Express.

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So we're going to leave it until later in the video.

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So we want to install Express and if we type LS Of course there isn't a node modules directory yet but

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if we do NPM install express I'll take a moment.

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This is definitely a bigger download than the other things that we've installed so far.

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I now have a safe LS a node modules directory or I really refresh my file tree.

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You see no modules I have express and instead of node modules there are a lot of directories.

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A lot of files and this is all of the logic all of the code that makes the framework that we don't have

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to write ourself.

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So we'll close out of that.

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And the next thing that we need to do of course is require expressed in our application so we'll do

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far.

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Express equals require express just like that.

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And that will then import the module express.

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But unlike the earlier libraries or packages we've seen like Cat me where we said var Cat me equals

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require Cat me and then to use it all we had to do was say Cat me.

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In this case Cat me only has one thing that it does one simple function just like knock knock jokes

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only had one function as well.

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Well Express has lots and lots of different methods so we can't just execute express like this.

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To use it although we will be executing it and saving it to a variable which most people call app.

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So var express equals require express that just includes all the contents of this express directory

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and then we execute it and save it to a variable called app that everything that we do with Express

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will be app dot and then some method that express comes with.

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Now that we have express installed and initialized it's always a good idea just to make sure that it

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works.

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So let's try running node apps.

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Yes.

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Nothing should happen as long as we don't get an error.

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That means that we're good to go.

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Now we're going to define our first route.

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We're going to make it very simple application.

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When you go to slash you're going to get a message that says hi.

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And when you go to slash goodbye or let's just do buy you'll get a message that says good bye.

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And then also do one more which is when you go to slash dog you get a message that says meow.

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So three different routes three different places we can make a request to and we can get three different

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responses depending on where we request.

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So the syntax for defining a route looks like this.

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We'll start with this first one.

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The high there and we write app dot gets an app to get takes two different parameters.

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The first one is the euro or the path which is slash.

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In this case because we're trying to make a route when a user makes a get request which is what they

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get here means we will see apt up posts later on and even update the leads and patch and put some of

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the other HTP verbs.

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But getting posts are the most common.

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So apt get when you get requests made to slash which is also called the root path or just the route

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.

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Then we want this code to run which is a callback function and this callback function takes two different

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arguments requests and response.

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Again those are whatever we want them to be called totally up to us.

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But you'll see this most often and I think in fact on the official express docs that's what they use

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req in rez.

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Some people actually type it all out request and response but reckon rise is much more common to see

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so reckon Reds are actually objects inside of this function request is an object that contains all the

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information about the request that was made that triggered this route and response will contain all

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of the information about what we're going to respond with.

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So I'll show you that in a little bit will cancel that log it will see what it looks like.

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But to start we're going to write rez dot send.

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Hi there.

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And this is just a way of responding with some text but if we go to the page of our app once we serve

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it once it started then we expect to get the text.

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Hi there printed out to us in the browser this isn't going to work just yet though.

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Because if I run this note app yes nothing happens because we're missing one really important part of

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code in Express.

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We actually have to write the code to tell it to listen for different requests to do that.

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EXPRESS gives us a method called listen.

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So all right.

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Apt up listen and then we need to provided the port to listen on and I'll show you in my example here

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.

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I was listening on port three thousand but because we're on cloud nine we have to do things a little

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bit differently.

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We need to listen on process that NVI ports.

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So all of this code will actually just return a number like 3000 except it returns the number of cloud

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nine server that we have to use.

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So this is a variable.

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It's called an environment variable and the environment variable that we're working with is called port

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.

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So this will return a number but we don't hardcoded the number in.

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It's coming from cloud nine.

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There's one other piece of information that we should pass in which is process that EMV IP.

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And this is a line that you can just copy and paste from app to app.

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We'll be using it at the bottom of every single application that we make with Express.

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So it's one of those just cookie cutter lines that we need to use.

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This tells express to listen on a particular port that cloud 9 wants to and a particular IP that cloud

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nine expects it to as well so to summarize we initialized express safety to the area will we defined

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a single route when we make a get request to slash.

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We should see a they're sent back in the response in our browser and just defining the route isn't enough

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.

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We then have to tell the app to listen on a particular port an IP address.

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And now we just need to start the server with node apps that will run the entire contents of the file

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.

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You'll see our cursor changes.

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We can actually type commands anymore because our server has started.

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There is one small thing we can do to improve this.

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So when it Control-C out of that and we can pass in callback function to APT listen as well.

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And inside of here we'll just you cancel that log server has started just like that and save it now

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going to clear and start the server again and we get this message that says server has started just

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so that it's clear what's happening with our consul now to visit this site unlike the local version

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that I showed with sublime and the dog demo where I went to local host Colan 3000 Clubine actually hosted

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online at your own you are well and you can find that by clicking on preview and click on Preview running

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application and that will open up a new tab.

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And if we want to we can just use the tab here.

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I prefer to copy the role and open up a new tab and paste that in so that I can actually just use it

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in the browser without having to go through cloud 9 is fake browser so close out of that and you'll

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see though my role is the name of my workspace web dev who camp dash my user name dot C-9 dot.

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So whatever you're serving in that workspace which right now is this one file apt.

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Yes instead of first express app will be at the row that is given to you for free automatically when

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you create a cloud nine workspace and more exciting than that.

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We can see that we get high there.

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It's working and making a request to the root of the server just slash.

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And I'm getting high there.

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And if we try doing something else like this you'll get a message that says cannot get that you are

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will this path that I added.

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So let's add in another out now.

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The exact same pattern.

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Let's do the buy route.

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So we want an app don't get slash.

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And then our function request response just like that.

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And we will send red dots and goodbye just like that and save that.

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Now if we go to slash buy and hit enter.

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You'll see that it still doesn't work.

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And that's because we have to restart the server.

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So any time we make some changes need to restart the server.

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For now I'm going to show you a tool that will help us so that we don't have to constantly restart it

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.

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But for now I need to do node Abdulle J.S. again save or refresh this time if we go to slash by.

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I now get my goodbye message and if I go to the root I get high there.

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So let's do one more now.

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Let's go back.

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So apt get sloshed dog or call back with requests and response and then instead of that we're going

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to respond.

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RAZ And meow.

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What was I thinking.

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Why did I say meow.

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All right well I'm going to go with it.

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Definitely should have female but if I start my server again I restarted Control-C to quit and they

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hit the up arrow and I run node after JSC again and I go back here I refresh.

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And now I go to slash dog get me out and I can go to slash by the gate goodbye and I can go to slash

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nothing and get high there.

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So that's all we're doing for this very first express app.

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Before we move on.

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I'm going to open up postman and test our application out.

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So we're going to make a get request and we'll do it to the slash dog route just to test it out and

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rather than local hosts 3000 slash dog we need to make a request to this you Arel slash dog.

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So I'm going to copy this and go back to postman and just paste that you are Ellen.

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And before we do anything else you know resize this and resize this window as well and we can close

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or shrink this down a bit it's going to make a request to this Web Dev Bootcamp dash learn with Colt

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C9 Daddy-O slash dog of course.

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This you also will match your own cloud 9 count.

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And what I'm going to do is instead of my app dog I'm going to add a Dalt log.

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And it's just going to say

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someone made a request to slash dog and we'll save that and this console blog is going to appear down

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here.

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It's not going to appear in the browser inside of the JavaScript debugging console.

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The front and con. It appears in the node console here that we have started by running node apps.

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Yes.

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So if I restart the server and I'll start by just showing you if I move this over here and I refresh

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the page let me go to another page and refresh.

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And now if I go to slash dogs or dog watch down here it says someone has made a request to Slashdot

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.

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So that's just to show you that that code is triggered as soon as we make a request and it's not only

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triggered by our browser but we can also trigger it by using postman which I'll show now.

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So all I need to do is hit enter here or send and we got another.

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Someone made a request to slash dog but also a full screen postman.

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Now let's look at what was sent back.

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So the body is just meow.

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I don't know what I was thinking I'd do it now but we got some text back meow and we can do the same

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thing by going to just the right path and sending a request and we get high there and we can also do

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slash by.

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And we also get the same thing.

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So this is to show you that these requests it doesn't matter where they originate from if it's from

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a browser.

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A phone with the browser if it's from a terminal somewhere or something like Postman it doesn't matter

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.

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Our server is just listening for any request that's a get request to three different routes.

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Dog by and the route route and when it gets one of those requests it will then respond with some simple

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text.

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All right.

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So that's all I wanted to cover in this first intro to express app.

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I know it's really really simple it hasn't amounted to much yet as an application but trust me the order

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that we're going in is very very deliberate.

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We're starting small and we're going to add one piece at a time the next few pieces that we'll add are

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responding with HQ mail files.

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So rather than read that send there's another method that we'll use to send an entire file of H.T. mail

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back and we'll also introduce a concept called Raut variables or path variables.

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OK I'll see you in the next video