Programming Tutorials

Node.js as a HTTP Server - Building from scratch - Tutorial for Beginners

By: William Alexander in node.js Tutorials on 2018-08-04  

This node.js tutorial is for a beginner to understand the basics of node.js from scratch. More specifically, this tutorial explores how node.js can be used as a HTTP server to handle HTTP requests and serve files. Since this assumes that you are just beginning to learn node.js, I will start from explaining what is node.js and how to install it and then continue with the step by step guide.

What is node.js?

First of all, it is good to know that node.js is free :). And it can be installed in almost all platforms including windows, linux, macos, unix etc. Although I am a linux fan (particularly ubuntu), in this tutorial we will use Windows as a development environment to learn. This is because, all of us use laptops or PCs to develop and it is always handy if everything required to code resides in our laptop for easy reference. However, the same can be achieved in an Ubuntu or mac system as well. Only the installation file will be different, the rest of the code will be same in all platforms. 

Node.js is a server platform and it is open source. And the good news is that all node.js code is written in JavaScript :) isn't that great? You can use Node.js for any of your back-end applications. However, in this tutorial we will use Node.js as a HTTP Server. Node.js differs from other HTTP servers in a sense that it use asynchronous programming. To illustrate this, let us take an example of how a typical http server functions. When PHP, JSP or ASP handles a request, it runs the server code such as reading the file, executing it and then finally responding to the request with a response. This is done synchronously. But since they are multi-threaded they can handle multiple requests simultaneously. But in node.js it is single threaded but since it uses asynchronous programming, it accepts requests sends the task to the file system and returns back to handle next request. This greatly improves memory-handling and it is non-blocking. In this tutorial we will see how this is done.

How to install node.js?

Installing node.js is the simplest step in this tutorial. Just visit node.js download page and download the LTS version which is currently 8.11.x. Download the appropriate file. For windows you can download the .msi file for 64-bit and run the installation file. Once it is installed, you can just open a command prompt and type node -v and it should show the version 8.11.x. That's it, you are ready to run node.js applications.

The next thing you would need is a proper IDE to develop and write code. Although you can use any text editor such as notepad++, I personally recommend Atom. Just visit Atom Download Page and download and run the installer. Atom is a beautiful and elegant code editor that is free and open source. You can use it to organize projects and write beautifully formatted and color coded scripts that is pleasing to look at and easy to understand.

Now that you have installed the node.js server and the atom IDE, you are ready to start programming.

Node.js as a HTTP server

It is important to note that node.js can be used to develop any of your backend workflows and logic using JavaScript and it is not a HTTP Server. But the beauty of node.js depends on its available modules which are nothing but JavaScript Packages. One such module is the 'http' module. So if you want to use node.js as a HTTP server then you have to use this 'http' module. Use 'require' keyword to include or import modules in a node.js script. First open a command prompt and go to c:\Users\yourusername\ and create a new folder named 'nodejstutorial'. cd (change directory) to nodejstutorial so that all your program files will be created in this folder.

var http = require('http');

Now open Atom or any other IDE of your choice and create a new project. This will create a new project under the current directory. Create a new file and copy the following code in it.

var http = require("http");

    res.end('This is my first node.js script');	

Save the file as 'first.js'. Congrats!!! You have created your first node.js script and it is going to be a HTTP server. To run this code, open a command prompt and change directory to c:\users\yourusername\nodejstutorial or the folder where you created this above script. Now just type 'node first.js'

c:\users\yourusername\nodejstutorial> node first.js

What you just did is to instruct node.js to execute the code from first.js. In first.js you created an instance of the http server to listen to port 8080. Therefore the node.js will continue to listen to port 8080 until you terminate by doing CTRL+C. To check your first script, open any browser and goto url http://localhost:8080/ and you should see the text 'This is my first node.js script' gets displayed in the browser.

Serving different content based on url

So far, you have made node.js to act as a HTTP server and serve a single page with some text. But of course, you would want node.js to do more and serve multiple pages instead of a single page. You can achieve this by using another module named 'url'. Let us create two files left.html and right.html with different text of course and let node.js serve these content depending on which url was requested by the user.

For this first create left.html in the same project (same folder)

<head><title>This is left header</title></head>
<h1>This is left header</h1>
<p>This is some left text</p>

Now create the right.html in the same project (same folder)

<head><title>This is right header</title></head>
<h1>This is right header</h1>
<p>This is some right text</p>

Now edit the first.js script so that the request page can be extracted from the url and then serve the right page content. For this, in addition to 'url' module we have to use the 'fs' module which is the file system module that handles file handling such as reading, writing, appending, deleting files. In this case, we just want to read the files left.html and right.html and get its content.

Open first.js and edit the script as below:

var http = require("http");
var url = require('url');
var fs = require('fs');

	var q = url.parse(req.url,true);
	var filename = "." + q.pathname;
	fs.readFile(filename, function(err,data){
			return res.end('404 File not found');

Save the file. Now that we have modified the code, go to the command prompt which we started in first step. Press CTRL+C to terminate the server if you have not done so. Once you are back to the command prompt, just press the up arrow to get the previous command which is 'node first.js' and press enter. This will refresh the code and re start the HTTP server. You can now go to the url http://localhost:8080/left.html or http://localhost:8080/right.html or http://localhost:8080/testnotfound to check the different content returned by node.js server.

In the above script the url is parsed and the filename is retrieved. The requested file is read using 'fs' module and its content is returned as response. If the file does not exist then a 404 file not found error is returned. By now you should be familiar with how node.js can be used as a HTTP server to handle http requests and serve multiple pages. Look forward to other tutorials that dives deeper into more complex use cases.

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