Node.js Module With Examples

This article will explain Node.js and its modules with examples, and we will create our own custom server using the Node.js application.

To understand and create the Node.js application, please download and install it from the official site: node.js

Node.js

According to official documentation,

Node.js® is a JavaScript runtime built on Chrome's V8 JavaScript engine for easily building fast and scalable network applications.
Node.js is free
Node.js runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)
Node.js uses JavaScript on the server
Node.js modules

Module in Node.js is a simple or complex functionality organized in single or multiple JavaScript files which can be reused throughout the Node. js application.

In short we can break large javascript files into multiple files and reuse it.

Let's create your first project in node.js application

Hello World

Step 1

Open command prompt and navigate to your project directory (My project directory is D:\Arvind\solution\nodesolution\nodeExamples).

Step 2

Type npm init and answer the following question as per the following details.

Step 3

To create a blank .js file type the below command (It will create blank index.js in our current directory).

type Nul > index.js

Step 4

Open index.js file in your editor (visual studio code) and write the below code.

console.log("Hello World")

Step 5

To run and see the ouput type node index.

node index

Since we had completed our first project in node.js application, let's see the node modules.

Node.js Module Types

There are basically three types of modules,

File based Modules
Core Modules
External or Third Party Modules

File based Modules

This types of modules are created locally in your node.js application. It includes different functionalities of your application in seperate files and folders.

The require function is used to import a module in nodes.js application.

Example

Create LocalModule.js file and insert the follwing code.

// create a variable calc that have four function add, subtract, multiply and divide.
const calc = {
// Add the two number
add: function (num1, num2) {
return num1 + num2
},
// Subtract the two number
subtract: function (num1, num2) {
return num1 - num2;
},
// multiply the two number
multiply: function (num1, num2) {
return num1 * num2;
},
// divide the two number
divide: function (num1, num2) {
return num1 / num2
}
};
// export the modules to consume on different modules.
module.exports.calc = calc;

To use the above functionality in a different module, create index.js and write the code

// To use custom module declare the code like this.
const myCalculation = require('./LocalModule.js');
// Declare two variable
const num1 = 5;
const num2 = 4;
// consume the existing function from LocalModule.js
console.log(`Addition of ${num1} and ${num2} is: ${myCalculation.calc.add(num1, num2)}`);
console.log(`Subtraction of ${num1} and ${num2} is: ` + myCalculation.calc.subtract(num1, num2));
console.log(`Multiply of ${num1} and ${num2} is: ` + myCalculation.calc.multiply(num1, num2));
console.log(`Divide of ${num1} and ${num2} is: ` + myCalculation.calc.divide(num1, num2));

Now type node LocalModule to see the ouput.

Core Modules

It is also known as (built in modules).

These core modules are compiled into its binary distribution and load automatically when Node.js process starts.

In order to use Node.js core or NPM modules, you first need to import it using require() function as shown below.

const variableName = require('module_name');
const path = require('path');

Example

Write the below code in CoreModule.js file.

// declare the core library file.
const path = require('path');
//Use the core library file.
console.log("Directory of index file: " + path.dirname(__filename));
console.log("Extension of index file: " + path.extname(__filename));
// check more detail on path library from here https://nodejs.org/dist/latest-v12.x/docs/api/path.html
// For rest of core libary https://nodejs.org/dist/latest-v12.x/docs/api/

To see the ouput type command node CoreModule

External or Third Party Module

As the name suggests it is a third party module which needs to install in order to use in your node.js application by using NPM (Node Package Manager).

It will create node_modules folder in your node application.

Example

To demonstrate third party or external modules, I have used the third party module https://www.npmjs.com/package/dota2-heroes which contains function random() and it gives the random hero's name wherever we call random function.

To use the above library first we have to install it and then use it by importing require('dota2-heroes') in your node application.

To install the library write the below command in your terminal.

npm i dota2-heroes

To consume the above library in your application, write below code in ThirdPartyModule.js file

//https://www.npmjs.com/package/dota2-heroes
// First install by using command npm i dota2-heroes
// To consume the above module
const names = require('dota2-heroes');
// call the existing method
const randomName = names.random();
// print the heroes
console.log("Heroes Name is :" + randomName);

To see the ouput type command node ThirdPartyModule

Create Custom Server using node.js

Let's create the custom server step by step.

Step 1

Open command prompt and create package.json file by using command

npm init

Step 2

Create blank index.js file by using command

type Nul > index.js

Step 3

Create file customserver.js and write the below code.

// import core library files
const httpOperation = require('http');
const fileOps = require('fs');
const path = require('path');
// declare two variables
const hostName = "localhost";
const port = 9999;
/**
* This method is used to create server by using http methods
*
* @param {*} request It will contains request data like. GET Method or POST method, URL.
*
* @param {*} response It will provide the response depends upon the request.
*
*/
const server = httpOperation.createServer((request, response) => {
// check method is 'GET method or not'
if (request.method === 'GET') {
let fileUrl;
// check the request url. If it constains only ('/') then navigate to index.html
if (request.url === '/') {
fileUrl = "/index.html";
} else { // if not then pass the requested url.
fileUrl = request.url;
}
// Now resolve the path by providing the complete file location
let filePath = path.resolve('./HTML' + fileUrl);
// Get the file extension
const fileExt = path.extname(filePath);
// check file is html file or not
if (fileExt === '.html') {
fileOps.exists(filePath, (isExists) => { // write the call back function if file exists or not
if (isExists) { // If requested file exist in filepath then show the index.html
response.statusCode = 200;
response.setHeader('Content-Type', 'text/html');
fileOps.createReadStream(filePath).pipe(response);
} else { // else show the file doesnot exist with 404 error.
showError(response, fileUrl, 'is not exist.');
}
});
} else {
// else show the file is not a HTML file with 404 error.
showError(response, fileUrl, 'is not HTML file.');
}
} else {
// else show the request method is not GET with 404 error.
showError(response, fileUrl, 'is not GET Method.')
}
});
/**
* This function is used to show error messages.
*
* @param {*} response Pass the response variable
* @param {*} fileUrl pass the file url
* @param {*} errorMsg pass the errorMsg
*/
function showError(response, fileUrl, errorMsg) {
response.statusCode = 404;
response.setHeader('Content-Type', 'text/html');
response.end('<html><body><h1>Error 404 ' + fileUrl + ' ' + errorMsg + '</h1></body></html>');
}
server.listen(port, hostName, () => {
console.log(`Server run at http://${hostName}:${port}`);
});

Step 4

Create index.html file under HTML folder and write below code.

Note

I have created simple index.html file for demonstration purpose.

<html>
<body>
<h1>
Welcome to node.js tutorial
</h1>
</body>
</html>

Step 5

Write one line code in package.json file under script tag "start": "node customserver"

Step 6

To start the server type the below command:

npm start

Step 7

To see the ouput browse http://localhost:9999 which shows 'welcome to node.js tutorial' on the page.

You can download all the source code from the attachment.