The role of a web server is to service the user's requests. The requests are expressed by clicking links, or occasionally by writing an url in the appropriate place and then hitting the enter key. The answer of the server is the response. The words request and response is the official http terminology.

In this section we shall make another server. Before we make applications you remember that we generally use npm init to create the configuration package.json interactively. Alter the suggested index.js starting point to whatever you call the JavaScript file that starts the application. Here we use main.js again. Put in some remarks fitting the project into the description. Finalizing that, the command will present the file content for your approval.

Your textbook does not use it on page 38, but we do start all Node.js application by using npm init -y.

{
  "name": "myg51",
  "version": "0.9.0",
  "description": "Server responding to requests",
  "main": "main.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Niels Müller Larsen <nmla@iba.dk> (http://dkexit.eu)",
  "license": "MIT"
}

Knowing one of the dependencies of the server/application we will build, let us see how to do that and get the configuration file updated in the process. On the command line we write, also for this project

npm i http-status-codes

The dependencies section of the configuration file is changed accordingly.

You already saw a sneak preview of a server in so many lines of code. Now we will do it again. This time with the necessary explanatory remarks. Create an application directory, step into it with cd myg51 and write:

"use strict";

const http = require("http");
const httpStatus = require("http-status-codes");
const hostname = "127.0.0.1";
const port = 3000;
const app = http.createServer();            // server as an obj

app.on("request", function (req, res) {     // eventhandler for "request"
    console.log("Log: Received an incoming request!");
                                            // prep response header
    res.writeHead(httpStatus.OK, {
        "Content-Type": "text/html; charset=utf-8"
    });
                                            // prep response body
    let responseMsg = "<h1>This Will Appear on the Screen</h1>";
    responseMsg += "<p><kbd>myg51</kbd> at your disposal</p>";
    res.write(responseMsg);                 // respond
    res.end();                              // sends response http
    console.log(`Log: Responded: ${responseMsg}`)
});

app.listen(port, hostname, function () {
    console.log(`Server running, and listening at http://${hostname}:${port}/`);
});