03 - Express code

In this module we'll make a simple Express server.

File Structure

Let's go inside of app.js in your server directory.

       Node-Server
            └── server
                └── .gitignore
                └── app.js

Basic Server Code

In app.js, go ahead and add the following code:

var express = require('express'); //1
var app = express(); //2

//3         //4
app.listen(3000, function(){
    console.log('App is listening on 3000.') //5
});

Analysis

Let's analyze the code:

1. Here we require the use of the express npm package that we've installed in our dependencies.

2. We create an instance of express. We're actually firing off a top-level express() function, a function exported by the Express module. This allows us to create an Express app.

3. app.listen will use express to start a UNIX socket and listen for connections on the given path. This method is identical to Node’s http.Server.listen().

4. The given path is localhost:3000.

5. We call a callback function when the connection happens with a simple console.log.

Running the Code

1. Open your terminal in VS Code. Make sure you are in the server directory.

2. Type in node app.js.

3. In your console/terminal window, you should see your console message:

   

   Don't worry about the error message right now. It won't affect anything.

4. When we go to http://localhost:3000/, we will see the application running like this:

screenshot

We'll explain this particular screenshot later.