Server.js

var express = require('express');
var app = express();
var fs = require("fs");
var bodyParser = require('body-parser');

// Create application/x-www-form-urlencoded parser
var urlencodedParser = bodyParser.urlencoded({ extended: false })
var authenticatedUser = null;
app.use(express.static('Front End'));

// Email validation funciton
function validateEmail(email)
{
    // using regular expression.
   	if (email.length > 0)
   	{
   		var re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
    	return re.test(email);
	}
	else
	 	return false;
}

// Password validation function
function validatePassword(pass)
{
	if (pass.length < 5)
		return false;
	else
		return true;
}

// Username validation function
function validateUsername(name)
{
	if (name.length > 0)
		return /^[a-zA-Z]*$/.test(name);
	else
		return false;
}

/**** This part to handle default request url= localhost:8081 ******/
app.get('/', function (req, res) {
  res.sendFile( __dirname + "/" + "homepage.html" );
})

app.get('/homepage.html', function (req, res) {
  res.sendFile( __dirname + "/" + "homepage.html" );
})

app.post('/login', urlencodedParser, function (req, res) {

  // Get the values of the input text email & password
  email = req.body.email;
  password = req.body.password;
  console.log(email);
  console.log(password);

  // Read JSON file containing the users to verify that the user is already registered and have access
  fs.readFile( __dirname + "/" + "users.json", 'utf8', function (err, data) {
    // Note that err here is for handling any error occuring in opening the file
    if (err)
    {
       return console.error(err);
   	}
    data = JSON.parse(data);
    var flag = 0;
    for (var user in data)
    {
      if(email == data[user].email)
      {
        flag = 1;
        authenticatedUser = user;
        break;
      }
      else
      {
        flag = 0;
      }
    }
    if(flag == 1)
    {
    	if (password == data[authenticatedUser].password)
    	{
    		res.sendFile( __dirname + "/" + "ProjectPh1V1.html");
    	}
    	else
    	{
    		res.sendFile( __dirname + "/" + "homepage.html");
    	}
    }
    // Handle invalid login by redirecting the user to the login page once again
    else {
    	res.sendFile( __dirname + "/" + "homepage.html");
    }
  });
 })

 app.post('/register', urlencodedParser, function(req, res)
 {
 	username = req.body.username;
 	email = req.body.email;
 	password = req.body.password;
 	console.log(username);
 	console.log(email);
 	console.log(password);

 	var f = 0
 	if (validateUsername(username))
 		f++;
 	if (validateEmail(email))
 		f++;
 	if(validatePassword(password))
 		f++;

 	if (f == 3)
 	{
 		// Add user to the JSON file database and show the homepage again
 		console.log('Invalid user registration input');
 		res.sendFile( __dirname + "/" + "homepage.html");
 	}
 	else
 	{
 		// Show error message and FREEZE MODEL  THIS IS NOT DONE YET           <----------------------------
 		console.log('Invalid user registration input');
 		res.sendFile( __dirname + "/" + "homepage.html");
 	}
 })

app.get('/ProjectPh1V1.html', function(req, res){
	res.sendFile( __dirname + "/" + "ProjectPh1V1.html" );
})

var server = app.listen(8081, function () {
	var host = server.address().address
	var port = server.address().port
	console.log("App listening at http://%s:%s", host, port)
})