Express

Initialize Express

const express = require('express');
const app = express();
 
// Access static files like CSS, JS and Images that are inside the public folder
app.use(express.static(__dirname + '/public'));
 
// Allows us to access the data of POST request
app.use(express.urlencoded({extended: true}));

URL Routing

app.get('/', function(req, res) {
	//Send back a File
	res.sendFile(__dirname + '/index.html');
});
 
app.post(['/', '/register'], function(req, res) {
	//Returns the data from the form
	console.log(req.body);
 
	//The values in String typecasting is required
	//Property name is the name of the input in the form
	var num1 = req.body.num1;
});
 
app.get('/failure', function(req, res) {
	//Redirect to a different route
	res.redirect('/');
});

Route Chaining

app.route('/article')
.get(function(req, res) {
	//Write code here
})
.post(function(req, res) {
	//Write code here
})
.delete(function(req, res) {
	//Write code here
});

Dynamic Routes

app.get('/post/:topic', function(req, res) {
	//Returns the value of :topic
	console.log(req.params.topic);
});
 
app.get('/post', function(req, res) {
	//Returns the data after the ? as an object
	console.log(req.query);
});

User Middleware

• The id here is the :id term that was part of URL. The value of the id is saved in val
• Such an middleware can be used to create a function that does some actions based on the value of the URL parameter

app.param('id', function(req, res, next, val) {
	//Note that the code needs to be returned else will be continuously run and be stuck here
	if(val > tours.length) {
		return res.send('Correct ID : ' + val);
		//next() is needed else the code will get stuck in this middleware
		next();
	}
});

• Middleware can bee also passed as first parameter for the requests to cause that middleware to be run for that route
• Here we have created a function called checkBody that is used to check the message that is received when the POST route is used

app.route('/article')
.get(function(req, res) {
	//Write code here
})
.post(checkBody, function(req, res) {
	//Write code here
});

Running the Server

Change 3000 to process.env.PORT || 3000 when deploying website

app.listen(3000, function() {
	console.log('Server running on localhost:3000');
});

Creating Router Object

1. tourRoutes.js

const router = express.Router();
 
// The app variable is changed to router
router.route('/')
.get(function(req, res) {
	//Write code here
})
.post(function(req, res) {
	//Write code here
});
 
router.route('/:id')
.get(function(req, res) {
	//Write code here
})
.post(function(req, res) {
	//Write code here
});
 
module.exports = router;

2. app.js

const tourRouter = require('./routes/tourRoutes');
 
// Mounting of the router
app.use('/api/v1/tours', tourRouter);
 
// Handling undefined routes (Error Handling)
app.all('*', function(req, res, next) {
	res.status(404).json({
		'status' : 'fail',
		'message': 'Route does not exist'
	});
});

Error Handling Middleware

• When these four parameters are used Express understands it’s an error handling middleware. Add this as the last middleware after all the routes, etc in the code

app.use(function(err, req, res, next) {
	err.status = err.status || 'fail';
	err.statusCode = err.statusCode || 500;
 
	res.status(err.statusCode).json({
		'status': err.status,
		'message': err.message
	});
});
 
 
// Use the middleware in the route where it is required
const err = new Error('Can't find such a path');
err.status = 'fail';
err.statusCode = 404;
					  
// When error object is passed to next() it will skip other middleware and go to the error handling middleware
next(err);