A basic HTTP server

A basic HTTP server

When I arrived at the point where I wanted to start with my first "real" Node.js application, I wondered not only how to actually code it, but also how to organize my code. 

Do I need to have everything in one file? Most tutorials on the web that teach you how to write a basic HTTP server in Node.js have all the logic in one place. What if I want to make sure that my code stays readable the more stuff I implement?

Turns out, it's relatively easy to keep the different concerns of your code separated, by putting them in modules.

This allows you to have a clean main file, which you execute with Node.js, and clean modules that can be used by the main file and among each other.

So, let's create a main file which we use to start our application, and a module file where our HTTP server code lives.

My impression is that it's more or less a standard to name your main file index.js. It makes sense to put our server module into a file named server.js.

Let's start with the server module. Create the file server.js in the root directory of your project, and fill it with the following code:

var http = require("http");

http.createServer(function(request, response) {
  response.writeHead(200, {"Content-Type": "text/plain"});
  response.write("Hello World");
  response.end();
}).listen(8888);

That's it! You just wrote a working HTTP server. Let's prove it by running and testing it. First, execute your script with Node.js:

node server.js

Now, open your browser and point it at http://localhost:8888/. This should display a web page that says "Hello World".

That's quite interesting, isn't it. How about talking about what's going on here and leaving the question of how to organize our project for later? I promise we'll get back to it.

Analyzing our HTTP server

Well, then, let's analyze what's actually going on here.

The first line requires the http module that ships with Node.js and makes it accessible through the variable http.


We then call one of the functions the http module offers: createServer. This function returns an object, and this object has a method named listen, and takes a numeric value which indicates the port number our HTTP server is going to listen on.


Please ignore for a second the function definition that follows the opening bracket of http.createServer.


We could have written the code that starts our server and makes it listen at port 8888 like this:

var http = require("http");
var server = http.createServer();
server.listen(8888);

That would start an HTTP server listening at port 8888 and doing nothing else (not even answering any incoming requests).


The really interesting (and, if your background is a more conservative language like PHP, odd looking) part is the function definition right there where you would expect the first parameter of the createServer() call.


Turns out, this function definition IS the first (and only) parameter we are giving to the createServer() call. Because in JavaScript, functions can be passed around like any other value.