Express JS: Routes, Middlewares, & MySQL Connection

Installation

npm install express

Create ‘Hello World’ Express App

First create a file “index.js”

const express = require('express')
const app = express()

app.get('/', function (req, res) {
    res.send("Hello World")
  })

app.listen(8000, ()=> {
	console.log('connected to backend')
})

Now Start Your APP

node index.js

Note: when running it, make sure you are in the backend folder (go with : cd backend)

Simplify this process with script:

Add this line inside script of package.json
	"start":"node index.js"
	
	now write "npm start" to run the server

For Continuously Running the Server

Install Nodemon

npm install nodemon

Now run with:

npx nodemon index.js

Simplify this process with script:

Add this line inside script of package.json
	"start":"nodemon index.js"
	
	now write "npm start" to run the server

Basic Routing, POST & DELETE

GET Request

app.get('/', function(req, res){
  res.send('This is a get request. I am fetching some data.')
})

POST Request

app.post('/', function(req, res){
  res.send('This is a post request. I am sending some data through a registration form.')
})

DELETE Request

Use Case: Suppose you have a list of fruits and you want to delete 2nd fruit.

DELETE http://localhost:3000/fruits/2

// Simple list of fruits with IDs
let fruits = [
  { id: 1, name: 'Apple' },
  { id: 2, name: 'Banana' },
  { id: 3, name: 'Mango' }
];

app.delete('/fruits/:id', (req, res) => {
  // Get ID from URL
  const id = parseInt(req.params.id); 

  // Remove the fruit with the given ID
  fruits = fruits.filter(fruit => fruit.id !== id);

  res.send(`Fruit with ID ${id} deleted!`);
});

ROUTES in a DIFFERENT FILE

File: /routes/users.js (For all GET, POST Requests for Users)

var express = require('express')
var router = express.Router()
 
router.get('/', (req, res) => {
 const users = [] // get from db
 res.send(users)
})
 
router.get('/:id', (req, res) => {
 const user = {} // get from db
 res.send(user)
})
 
router.post('/', (req, res) => {
 const user = req.body // save user to db
 res.send({status: 'success'})
})
 
module.exports = router

ADDING ROUTES FROM: /routes/users.js

app.use('/user', require('./routes/user'));

Middlewares

for middlewares

// Built-in middleware for parsing JSON requests
app.use(express.json());

// Serve static files
app.use(express.static(‘public’));

MySQL Connection

I have explained in this article on how to connect MYSQL with the ExpressJS/NodeJS.