A brief intro to Node.js

This is a topic I’ve been meaning to approach for a while now. As it happens, one of my college courses – Web Applications – requires a project built using Node.js, so what better time to tackle this.

I had mentioned Node.js in a previous post, where I was talking about the various environments JavaScript can be run in. This post won’t go into the history or specifics of Node.js; the main exercise will examine the various items found in the sample code for creating a simple Node.js server – which will explore and detail node specific aspects as well as JavaScript patterns used. The code can be found on the About page on the Node.js site:

const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World\n');
});

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

Play by play

The very first line of code, allows us to import the module ‘http’.

const http = require('http');

This is the implementation method that is specified in CommonJS, which is an ecosystem for JavaScript outside the browser. This is a synchronous system which allows importing of modules or files; since everything will be on the server side. This allows us to import the module http.

The next two lines set the IP address of the localhost (the machine you are currently on) and the port to listen to for incoming requests.

const hostname = '127.0.0.1';
const port = 3000;

Immediately following that, the createServer() method is called on the http instance we created on the first line. Which is then assigned to a constant called server.

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World\n');
});

This is passed a call back function with two parameters and uses an arrow function (read more about it here [1] [2]). This createServer() method will be invoked by an incoming event, in this case web requests. The req parameter will contain all the incoming request’s details. The res parameter will handle the response which will be sent out. In this case it’s setting its statusCode to 200, which signifies that the request was handled successfully. After which the response’s header information is set to indicate it’s content which in this case is plain text. And finally some plain text output is shown while closing the response – this will be displayed in the browser.

The final section of the code the reference to the server, which points to the http.createServer() call, is set to listen on the port and host IP address set at above.

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

The arrow function will display the message indicated while the server is running in the node.js environment giving us a visual that things are working.

There you go, this was just a quick run down to help try and elucidate, both for me and anyone reading this, what is happening within this simple node.js server code. Stay tuned for more practical topics on the matter.