node.js: HelloWorld application

Step 1: Create package.json file.

Create a folder HelloWorld.

Open terminal, go inside 'HelloWorld directory and execute the command 'npm init -y'. It creates a default package.json file.

$npm init -y
Wrote to C:\Users\krishna\HelloWorld\package.json:

{
  "name": "HelloWorld",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

Step 2: Install express dependency by executing the below command.

npm install --save express

You should execute the above command from the directory, where your package.json file located. This command downloads the express module from Internet and update the package.json file with express dependency.

After executing the command, package.json looks like below.

{
  "name": "HelloWorld",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.16.4"
  }
}

After executing the above command, you can observe below two changes.

a.   There is a file package-lock.json file is created, it contain all the dependencies required by express

b.   node_modules folder is created. All the downloaded dependencies are placed in this folder.

Step 2: Create index.js file in the same place where your package.json located.

index.js

//Load express module
const express = require('express');

//Put new Express application inside app variable
const app = express();

const port = 8080;

//When user hits the home page, then the message prints in browser.
app.get('/', (req, res) => res.send('Welcome to Node.js Programming'))

app.get('/time', (req, res) => res.send(new Date().toString()))

app.get('/welcome', (req, res) => {
	var userName = req.query.name
	res.send("Hello Mr."+ userName)
})

app.get('/welcome/:userName', (req, res) => {
	res.send("Hello Mr."+ req.params.userName)
})

// Start the express application on port 8080 and print server start message to console.
app.listen(port, () => console.log(`Application started listening on port ${port}!`));

app.get('/', (req, res) => res.send('Welcome to Node.js Programming'))

Above snippet handle the requests to home page.

app.get('/time', (req, res) => res.send(new Date().toString()))

Above snippet handle the request uri /time

app.get('/welcome', (req, res) => {

         var userName = req.query.name

         res.send("Hello Mr."+ userName)

})

Above snippet handle the request uri /welcome

app.get('/welcome/:userName', (req, res) => {

         res.send("Hello Mr."+ req.params.userName)

})

Above snippet handle the request uri /welcome/{SOME_NAME}

Open terminal and execute the command ‘node index.js’ to start the application.

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