Web Application

In this chapter, we’re going to learn web programming similar to PHP but we’ll implement it using Node.js. There are a lot of web frameworks for Node.js. For our scenario, we’ll use a basic HTTP Node.js module and Express.js.

Getting Started

Node.js provides http modules to manipulate and handle the HTTP request and response. You can read this API on http://nodejs.org/api/http.html.

How to get started? Let's write this code:

Save this code into a file, for instance, web-demo1.js.

Now we start to run this application:

When executing this application for the Windows platform, you will get the form dialog shown in Figure 54. It’s better to check Private Network and then click Allow access.

The sample of the program output can be seen in Figure 55. Now you can open a browser and write the URL:

Then you will get a response in the browser as shown in Figure 56.

Figure 54: Confirming from Windows Firewall to open a port

Figure 55: Executing a simple web application

Figure 56: Accessing a web application using a browser

To work with web applications:

• First, load the HTTP module.
• Create a web server by calling createServer()
• We get the request and response objects (req, res)
• Handle the request and response from the client using these objects.
• Call end() to close sending the response to the client.
• We call listen() with a port parameter, for example 8084, to activate the listening process.

To stop the application, press Ctrl+C.

Manipulating an HTTP Header

We can get header information from a client request and send a response with a custom header.

We can get header information from a client request from req.headers directly. We can also set a custom header attribute by calling setHeader() from the response object (res).

Here is sample code for manipulating an HTTP header:

Run this code and open the browser application. Send a request to the server, for instance http://localhost:8084/. Then look at your console application. You will get a program output as shown in Figure 57.

Figure 57: Printing information about HTTP request header

Handling Page Requests

In the previous section, we learned how to create simple web application. Now we’ll continue to explore the HTTP module.

We can handle page requests from the client, for example:

• page /
• page /customer
• page /admin

To handle these page requests, we can check them through a request object and call the url attribute. If it matches with your expectations, then you can do something in your code.

Let’s write a complete simple application. Here is the sample code:

Run this code and open browser application. Try to request the server, for example http://localhost:8084/customer/. We will get the response shown in Figure 58.

Figure 58: A page responding to Node.js

Working with HTTPS

In this section, we’ll work with HTTPS for Node.js. First, we should have an SSL Certificate. You can buy it or create a self-signed certificate.

I would like to share how to create a self-signed certificate using openssl. Download openssl for your platform on http://www.openssl.org. For the Windows platform, you can download the setup file on http://slproweb.com/products/Win32OpenSSL.html.

After installed, try to open CMD and type the following:

You will get the prompt > in your console.

If you got a warning message as follows:

Then try to type this in your console:

Change the path of the file openssl.cfg. You can put it on the Environment Variables in the Windows OS. You can see this in Figure 59.

Figure 59: Setting OPENSSL_CONF

First, we generate a private key with 1024 length and store it to a file called myserver.key.

Open your console CMD and be sure you are running it as the administrator. Type this script:

If you still failed, you should run your CMD with administrator privileges. If successful, you will get a response as shown in Figure 60. Entry your pass phrase for the SSL key.

Figure 60: Creating an SSL key

Furthermore, we create a certificate file, called myserver.csr. Type this script:

Enter all fields. The sample response can be seen in Figure 61.

Now we need to sign our certificate. This means we are creating a self-signed certificate. Type the following commands:

Enter the pass phrase. You can see a sample of the console output in Figure 62.

Figure 61: Creating a certificate file

Figure 62: Signing a certificate file

Now we can integrate our previous code (HTTP) with a certificate file to apply HTTPS.

Add certificate information on options objects such as key file, certificate file, and pass phrase. Here is the sample code:

Run this code. Then open your browser and write https://localhost:8084/.

Because we used a self-signed certificate, we get a warning message from our browser as shown in Figure 63.

Click Continue to this website and then you will get a response from the Node.js application, shown in Figure 64.

Figure 63: Warning message for self-signed certificate usage

Figure 64: Web application with HTTPS

Express.js

In the previous section, we used an HTTP module that is a part of the Node.js standard modules. We can use the Express.js library web framework. You get further information about Express.js from the official website, http://expressjs.com/. Here is a list of features:

• Robust routing
• Redirection helpers
• Dynamic view helpers
• Application level view options
• Content negotiation
• Application mounting
• Focus on high performance
• View rendering and partials support
• Environment based configuration
• Session-based flash notifications
• Built on Connect middleware
• Executable for generating applications quickly
• High test coverage

These features could help you to accelerate web development and save development time.

Installation

The simple way to install Express.js is by using your npm manager. Before executing, your computer has already connected with the internet.

Type this command in your CMD:

You also can install it globally.

If it is successful, you will see the response as shown in Figure 65.

Figure 65: Installing Expressjs

Now we’re ready to write code using Express.js.

Getting Started

We start to write a simple program using Express.js. We will create a web application.

Let’s write this code:

First, we include the Express.js module by calling require(‘express’). After that, we create the server object by instantiating the server object.

Furthermore, we create a response handler.

At the end of code, we run a code listener on port 8084.

Now run it and open the browser. Write the URL http://localhost:8084/. You will get a response from the app as shown in Figure 66.

Figure 66: Getting a response from an Express.js app in browser

Handling Page Requests

To handle page requests in Express.js, you can call get() with the URL path as the parameter.

We can add multiple request handlers in our code, for instance, ‘/customer’ and ‘/admin’ requests. You can write this sample code as follows:

Run this code and open your browser with writing URL http://localhost:8084/customer/. You will get a response from the customer page handling of the Node.js app, shown in Figure 67.

Figure 67: Response to /customer request from Expressjs app

Express.js with HTTPS

We can implement HTTPS in Express.js. It uses the HTTP Node.js standard module so you can handle it the same way as the HTTPS server.

Run this code. You get the same response, show in Figure 68.

Figure 68: Express.js app with HTTPS