Node.JS Hello World

Node.JS Hello World

Introduction

We will start our Node.JS journey with a simple hello world application. Our application will not do much but will lay a solid foundation that will make it easy for us to learn Node.JS.

In this tutorial, we will create two simple hello world applications. One that displays the out in the console and the other that displays the information in the web browser.

Topics to be covered

We will cover the following topics in this tutorial;

• Tutorial Pre-requisites
• Create package.json using npm
• Node.JS Hello World Console Application
• Node.JS Hello World Web Application

Tutorial Pre-requisites

For you to successfully complete this tutorial, you will need to know the following.

• You have already installed the latest version of Node.JS. If you haven’t yet done so then read the previous tutorial that guides you on how to download and install Node.JS
• Command line / terminal – Node.JS makes heavy use of the command line
• Active internet connection – we need to download packages from the internet
• A text editor / IDE – you need it to write code
• JavaScript basic skills – you don’t need to be a JavaScript ninja to successfully complete this tutorial. Just the basics
• A web browser

Create package.json using npm

I am using windows operating system but you will still be able to follow the tutorial using any other operating system.

Open the command prompt and browse to drive C. feel free to use any drive of your choice

Run the following command to create a directory node. This directory will be used to store our applications

mkdir node

let’s now browse into the new directory using the following command

cd node

run the following command to create a directory for our application

mkdir hello-world

Run the following command to access the new directory hello-world

cd hello-world

Run the following command

npm init

Fill in the answers to the utility questions. Note: the utility always has sensible defaults. You just have to press the enter key to accept the default setting. You will however, need to enter the description, entry point and author name as shown below

The above command will create a package.json file in your project directory.

Open package.json file.

You will get the following information

{
  "name": "hello-world",
  "version": "1.0.0",
  "description": "A humble introduction to NodeJS app development",
  "main": "app.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Rodrick Kazembe",
  "license": "ISC"
}

Node.JS Hello World Console Application

Let’s start with a very basic app.

Create a new file app.js in the directory C:\node\hello-world\

Add the following code

console.log("Hello World!");

HERE,

• console.log("Hello World!"); this line calls the log method of the console class. Console is a global module that provides simple debugging console that is similar to the one JavaScript console in web browsers. "Hello World!" is the parameter that is passed to the log method.

Let’s now run our application.

Go back to the console.

Browse to the application directory

Run the following command

node app.js

HERE,

• node app.js the node command executes the JavaScript file app.js. Note: it is not necessary to specify the file extension. By default, Node.JS assumes the file extension is .js. You can run the above command as node app

You will get the following results.

Hello World!

Congratulations. You just created your first nodejs application.

What if we want to accept some user input and display it in our hello message? How do we do that? We can use the global module process that contains information about the currently running Node.JS process

Add the following code to app.js

console.log();
console.log(process.argv);

HERE,

• console.log(); prints a blank line
• console.log(process.argv); displays an array of data that contains the command line arguments.

Let’s now run our application in the console.

node app --name=Rodrick

You will get the following results

[ 'C:\\Program Files\\nodejs\\node.exe',
  'C:\\node\\hello-world\\app',
  '--name=Rodrick' ]

Note: we have the variable name with the value of Rodrick

Let’s now grab the command line argument and display it in the message that is returned to the user.

Replace the code for app.js with the following

function getArgument(argument){
    var index = process.argv.indexOf(variable);

    return (index === -1) ? null : process.argv[index + 1];
}

var name = getArgument('--name');

var message = name ? "Hello " + name : "Hello World";

console.log(message);

HERE,

• function getArgument(argument){…} defines a function that accepts the command line argument name. The function returns null if the argument name is not found, if the value if found, the function returns the value of the argument
• var name = getArgument('--name'); calls the getArgument function and passes in –name as the parameter. The result of the function is stored in the name variable
• var message = name ? "Hello " + name : "Hello World"; assigns the message Hellow World to the message variable if the name is null. If it is not null then the message Hello name variable value is assigned to the message variable.
• console.log(message); logs the information in the console

Let’s now test our application.

Run the following command

node app

You will get the following results

Hello World

Let’s now specify the name argument

node app --name "Amanda Kazembe"

You will get the following results

Hello Amanda Kazembe

You can find more information about Node.JS API from the official documentation

https://nodejs.org/api/index.html

You can bookmark it for easy reference.

Node.JS Hello World Web Application

Let’s now create a simple web based hello world application. Let’s create a new file that we will name web.js

The web based application will involve the following steps.

1. Import modules: Use the require directive to load Node.js packages.
2. Create server: A server which will listen to client's requests.
3. Read request and return response: The server created in step will read the HTTP request made by the client which can be a browser or a console and return response.

Open web.js file and add the following code

var http = require("http"); 

var port = 3000;

http.createServer(function(reqst, resp) { 
    resp.writeHead(200, {'Content-Type': 'text/plain'}); 
    resp.end('Hello World!'); 
}).listen(port); 

console.log('Load http://127.0.0.1:' + port + ' and watch the magic');

HERE,

• var http = require("http"); require is used to import the http module. The web uses http that’s why we have to import this module
• var port = 3000; defines a variable port and assigns a value of 3000 to it. This is the port number that the server will use.
• http.createServer(function(request, response) {…} calls the createServer method of the http class and passes in an anonymous function as an argument. The anonymous function has two variables request and response. The request variable contains information about the client request. The response object is used to create the response that is sent back to the web browser.
• response.writeHead(200, {'Content-Type': 'text/plain'}); sets the HTTP status of 200 and a header Content-Type with a value of text/plain.
• response.end('Hello World!'); sends the response hello World! To the browser
• http.createServer(…).listen(port); starts listening on the port specified by the value of the variable port.
• console.log('Load http://127.0.0.1:' + port + ' and watch the magic'); logs a message that shows the server URL that you can use to access the app from the browser.

Load the following URL

http://127.0.0.1:3000/

You will get the following message in the browser

Hello World!

Summary

In this tutorial, we learnt how to create two simple basic Node.JS applications. Our applications didn’t do much but they give us an idea and feel of Node.JS applications.

What’s Next?

The next tutorial is Node.JS Database MySQL. The tutorial will show you how to Node.JS application that can create, read and update and delete data from MySQL database.

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Tutorial History

Tutorial version 1: Date Published 2016-08-02