Question 1. Create a CLI for counting the number of words in a file specified.

javascript Copyconst { Command } = require('commander');
const fs = require('fs')
const program = new Command();

program
  .name('CountWordsCLI')
  .description('CLI to counts the number of words inside the file specified')
  .version('0.8.0');

program.command('count')
  .description('Counting the words in the file')
  .argument('<file>', 'file to count')
  .action((file) => {
    fs.readFile(file,'utf-8',(err,data) => {
      if (err){
        console.log(err);
      }else{
         const words = data.trim().split(/\s+/).filter(Boolean);
         console.log(`There are ${words.length} words in ${file}`);
      }
    });
  });
  
program.parse();

Question 2. Create a CLI for doing the CRUD operation in the To-Do List (which is a file).

javascript Copy#!/usr/bin/env node
const { Command } = require('commander');
const fs = require('fs');
const path = require('path');

const program = new Command();
const filePath = path.join(__dirname, 'todos.json');

// Ensure file exists
if (!fs.existsSync(filePath)) {
  fs.writeFileSync(filePath, JSON.stringify([]));
}

// Helper: Read todos
function readTodos() {
  return JSON.parse(fs.readFileSync(filePath, 'utf-8'));
}

// Helper: Save todos
function saveTodos(todos) {
  fs.writeFileSync(filePath, JSON.stringify(todos, null, 2));
}

program
  .name('todo-cli')
  .description('A CLI for managing a To-Do list')
  .version('1.0.0');

// CREATE
program
  .command('add')
  .description('Add a new to-do item')
  .argument('<task>', 'Task description')
  .action((task) => {
    const todos = readTodos();
    todos.push({ id: Date.now(), task, done: false });
    saveTodos(todos);
    console.log(`✅ Added: "${task}"`);
  });

// READ
program
  .command('list')
  .description('List all to-do items')
  .action(() => {
    const todos = readTodos();
    if (todos.length === 0) {
      console.log("📭 No tasks found.");
    } else {
      todos.forEach((t, i) => {
        console.log(`${i + 1}. [${t.done ? '✔' : ' '}] ${t.task} (ID: ${t.id})`);
      });
    }
  });

// UPDATE
program
  .command('update')
  .description('Update a to-do item')
  .argument('<id>', 'Task ID')
  .argument('<newTask>', 'Updated task description')
  .action((id, newTask) => {
    const todos = readTodos();
    const index = todos.findIndex(t => t.id == id);
    if (index === -1) {
      console.log(`❌ Task with ID ${id} not found.`);
      return;
    }
    todos[index].task = newTask;
    saveTodos(todos);
    console.log(`✏ Updated task ID ${id} to "${newTask}"`);
  });

// DELETE
program
  .command('delete')
  .description('Delete a to-do item')
  .argument('<id>', 'Task ID')
  .action((id) => {
    let todos = readTodos();
    const initialLength = todos.length;
    todos = todos.filter(t => t.id != id);
    if (todos.length === initialLength) {
      console.log(`❌ Task with ID ${id} not found.`);
      return;
    }
    saveTodos(todos);
    console.log(`🗑 Deleted task with ID ${id}`);
  });

// MARK AS DONE
program
  .command('done')
  .description('Mark a to-do item as done')
  .argument('<id>', 'Task ID')
  .action((id) => {
    const todos = readTodos();
    const task = todos.find(t => t.id == id);
    if (!task) {
      console.log(`❌ Task with ID ${id} not found.`);
      return;
    }
    task.done = true;
    saveTodos(todos);
    console.log(`✔ Task ID ${id} marked as done.`);
  });

program.parse();

Middlewares

Question 1 - RequestCount

You have been given an express server which has a few endpoints. Your task is to create a global middleware (app.use) which will maintain a count of the number of requests made to the server in the global requestCount variable.

javascript Copyconst express = require('express');
const app = express();

let requestCount = 0;

app.use(function(req, res, next){
    requestCount = requestCount + 1;
    next();
})

app.get('/user', function(req,res){
    res.status(200).json({ name : 'john'})
});

app.post('/user', function(req,res){
    res.status(200).json({ msg : 'created dummy user' });
});

app.get('/requestCount', function(req, res){
    res.status(200).json({ requestCount });
})


app.listen(3000);

Question 2 - Rate-limitter

You have been given an express server which has a few endpoints. Your task is to create a global middleware (app.use) which will rate limit the requests from a user to only 5 request per second

If a user sends more than 5 requests in a single secound, the server should block them with a 404. User will be sending in their user id in the header as 'user-id'. You have been given a number0fRequestForUser object to start off with which clears every one second.

javascript Copyconst express = require('express');
//const { use } = require('react');
const app = express();

let number0fRequestForUser = {};
setInterval(() => {
    number0fRequestForUser = {};
}, 1000)


app.use(function(req, res, next){
    const userId = req.headers["user-id"];
    if(number0fRequestForUser[userId]){
        number0fRequestForUser[userId] = number0fRequestForUser[userId] + 1;
        if(number0fRequestForUser[userId] > 5){
            res.status(404).send("no entry");
        } else{
            next();
        }
    } else {
        number0fRequestForUser[userId] = 1;
        next();
    }
});

app.get("/", (req, res) => {
  res.send("Welcome! Your request is allowed.");
});

app.listen(3000);

Question 3 - ErrorCount

You have been given an express server which has a few endpoints.

Your task is to

Ensure that if there is ever an exception, the end user sees a status code of 404

Maintain the errorCount variable whose value should go up every time there is an

exception in any endpoint.

javascript Copyconst express = require('express')
const app = express();
let errorCount = 0;
    
app.get('/user', function(req, res){
    throw new Error("User not found");
    res.status(200).json({ name : 'john'});
})

app.post('/user', function(req, res){
    res.status(200).json({ msg: 'created dummy user'});
});

app.get('/errorCount', function(req, res){
    res.status(200).json({ errorCount});
});

// error handling middleware
 app.use(function(err, req, res, next ){
    res.status(404).send({})
    errorCount = errorCount + 1;
 })

app.listen(3000);

module.exports = app;

Question - 4

Calculator with http server.

javascript Copyconst express = require('express');
const app = express();

app.get("/sum/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a+b
    })
});

app.get("/multiply/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a*b
    })
});

app.get("/divide/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a/b
    })
});

app.get("/subtract/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a-b
    })
});


app.listen(3000)

Question 5 - Create a middleware function that logs each incoming request’s HTTP method, URL, and timestamp to the console.

javascript Copy//Create a middleware function that logs each incoming request’s HTTP method, URL, and timestamp to the console.


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

function logger(req, res, next){
    console.log("Method is " + req.method)
    console.log("Url is " + req.hostname)
    console.log(new Date());
    next()
}

app.use(logger)

app.get("/sum/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a+b
    })
});

app.get("/multiply/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a*b
    })
});

app.get("/divide/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a/b
    })
});

app.get("/subtract/:a/:b",function(req,res){
    const a = parseInt(req.params.a)
    const b = parseInt(req.params.b)

    res.json({
        answer: a-b
    })
});


app.listen(3000)

Authentication

Question 1 - Authentication with token logic written by me.

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

app.use(express.json());

const users = [];

function generateToken(){
    let options = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'];
    let token = "";

    for(let i = 0; i < 32; i++){
        token += options[Math.floor(Math.random() * options.length)];
    }

    return token;
}

app.post("/signup", function(req, res){
    const username = req.body.username;
    const password = req.body.password;

    users.push({
        username: username,
        password: password
    })

    res.json({
        message: "You are signed up"
    })
})

app.post("/signin", function(req, res){
    const username = req.body.username;
    const password = req.body.password;
    let foundUser = null;

    for(let i = 0; i < users.length; i++){
        if(users[i].username === username && users[i].password === password){
            foundUser = users[i];
            break;
        }
    }

    if(foundUser){
        const token = generateToken();
        foundUser.token = token;
        res.json({
            message: "You are signed in",
            token: token
        })
    } else{
        res.status(403).send({
            message: "Invalid username or password"
        })
    }
})

app.get("/me", function(req,res){
    const token = req.headers.token;
    let foundUser = null;

    for(let i=0; i<users.length; i++){
        if(users[i].token == token){
            foundUser = users[i]
        }
    }
    if(foundUser){
        res.json({
            username: foundUser.username,
            password: foundUser.password
        })
    }else{
        res.json({
            message: "token invalid"
        })
    }
})

app.listen(3000);

Question 2 - Replace token logic with the JWT(Json web tokens)

javascript Copyconst express = require('express')
const app = express();
const jwt = require('jsonwebtoken');
//const { use } = require('react');
const JWT_SECRET = "karanilovekaran"

app.use(express.json())
const users = []

app.post("/signup", function(req, res){
    const username = req.body.username;
    const password = req.body.password;

    users.push({
        username: username,
        password: password
    })

    res.json({
        message: "You are signed up"
    })
})

app.post("/signin", function(req, res){
    const username = req.body.username;
    const password = req.body.password;
    let foundUser = null;

    for(let i = 0; i < users.length; i++){
        if(users[i].username === username && users[i].password === password){
            foundUser = users[i];
            break;
        }
    }

    if(foundUser){
        const token = jwt.sign({
            username : username
        }, JWT_SECRET);  // convert their username over to a jwt

        //foundUser.token = token;
        res.json({
            message: "You are signed in",
            token: token
        })
    } else{
        res.status(403).send({
            message: "Invalid username or password"
        })
    }
})

app.get("/me", function(req,res){
    const token = req.headers.token;
    const decodedInformation = jwt.verify(token, JWT_SECRET)
    const username = decodedInformation.username


    let foundUser = null;

    for(let i=0; i<users.length; i++){
        if(users[i].username == token){
            foundUser = users[i]
        }
    }
    if(foundUser){
        res.json({
            username: foundUser.username,
            password: foundUser.password
        })
    }else{
        res.json({
            message: "token invalid"
        })
    }
})

app.listen(3000);

Question - 3 Create a middleware called auth that verifies if a user is logged in and ends the request early if the user is not logged in. Also add the frontend for signup signin and logout.

javascript Copy// Create a middleware called auth that verifies if a user is logged in and ends the request early if the user is not logged in.

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

const jwt = require('jsonwebtoken');

const JWT_SECRET = "ilovekaran"

app.use(express.json())
const users = [];

function logger(req, res, next){
    console.log(req.method + " request came")
    next();
}

app.get("/", function(req,res){
    res.sendFile(__dirname + "/public/index.html")
})

app.post("/signup", logger,function(req, res){
    const username = req.body.username;
    const password = req.body.password;
    
    users.push({
        username: username,
        password: password
    })

    res.json({
        message: "You are signed up"
    })

})

app.post("/signin", logger, function(req, res) {
    const username = req.body.username;
    const password = req.body.password;

    let foundUser = null;

    for (let i = 0; i < users.length; i++) {
        if (users[i].username === username && users[i].password === password) {
            foundUser = users[i]
        }
    }

    if (!foundUser) {
        res.json({
            message: "Credentials incorrect"
        })
        return 
    } else {
        const token = jwt.sign({
            username: foundUser.username
        }, JWT_SECRET);

        res.header("jwt", token)
        
        res.json({
            token: token
        })
    }
})
function auth(req, res, next){
    const token = req.headers.token
    const decodedData = jwt.verify(token, JWT_SECRET);

    if(decodedData.username){
        req.username = decodedData.username
        next()
    }else{
        res.json({
            message: "You are not logged in"
        })
    }
}

app.get("/me", auth, logger, function(req,res){
    let foundUser = null;

    for(let i =0; i<users.length; i++){
        if(users[i].username === req.username){
            foundUser = users[i];
        }
    }

    res.json({
        username: foundUser.username,
        password : foundUser.password
    })
})

app.listen(3000)

html Copy<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Auth Website</title>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/axios/1.7.7/axios.min.js"></script>

    <script>
        async function signup(){
           const username = document.getElementById("signup-username").value;
           const password = document.getElementById("signup-password").value;

           await axios.post("http://localhost:3000/signup",{
              username: username,
              password: password
           })
           alert("You are signed up")
        }

         async function signin(){
           const username = document.getElementById("signin-username").value;
           const password = document.getElementById("signin-password").value;

           const response = await axios.post("http://localhost:3000/signin",{
              username: username,
              password: password
           })
           localStorage.setItem("token", response.data.token)
           alert("You are signed in")
        }
         
        async function getUserInformation(){
           const response = await axios.get("http://localhost:3000/me",{
                headers: {
                    token: localStorage.getItem("token")
                }
            })
            document.getElementById("information").innerHTML = "Username: " + response.data.username + " Password: " + response.data.password;
        }
        getUserInformation();

        function logout(){
            localStorage.removeItem("token");
        }
   </script>
</head>
<body>
    <div>
        SignUp
        <input id="signup-username" type = "text" name = "username" placeholder="username">
        <input id="signup-password" type = "password" name = "password" placeholder="Password">
        <button onclick="signup()">Submit</button>

    </div>
    <div>
        SignIn
        <input id="signin-username" type = "text" name = "username" placeholder="username">
        <input id="signin-password" type = "password" name = "password" placeholder="Password">
        <button onclick="signin()">Submit</button>

    </div>
    <div>
        UserInformation:
        <div id="information"></div>
    </div>
    <div>
        <button onclick="logout()">Logout</button>
    </div>
</body>
</html>

Database-

Todo application with jwt authentication-

DB.js

javascript Copyconst mongoose = require("mongoose")
const Schema = mongoose.Schema
const ObjectId = mongoose.ObjectId;

const User = new Schema({
    email: {type: String, unique: true},   
    password: String,
    name: String
})

const Todo = new Schema({
    title: String,
    done: Boolean,
    userId: ObjectId
})

const UserModel = mongoose.model('users', User)
const TodoModel = mongoose.model('todos', Todo)

module.exports= {
    UserModel: UserModel,
    TodoModel: TodoModel
}

index.js

javascript Copyconst express =  require('express')
 const { UserModel, TodoModel } = require("./db");
 const jwt = require("jsonwebtoken");
const { default: mongoose } = require('mongoose');
 const JWT_SECRET = "asdadslsg@123"

 mongoose.connect("mongodb+srv://titkaran09_db_user:WCFZpLejg1DhPUpN@cluster01.qc0er3j.mongodb.net/Todos")
 const app = express()

 app.use(express.json());

 app.post("/signup", async function(req, res){

      const email = req.body.email;
      const password = req.body.password;
      const name = req.body.name;


      await UserModel.create({
        email: email,
        password: password,
        name: name

      })

      res.json({
        message: "You are logged in"
      })
 });
 

 app.post("/signin",async function(req, res){
       const email = req.body.email;
       const password = req.body.password;
       
       const user = await UserModel.findOne({
        email: email,
        password: password
       })
      
       console.log(user)

       if(user){
        const token = jwt.sign({
            id: user._id.toString()
        }, JWT_SECRET);
        res.json({
            token: token
        })
       } else{
        res.status(403).json({
            message: "Incorrect credentials"
        })
       }

 });
 
 app.post("/todo", auth,  function(req, res){
     const userId = req.userId;
     const title = req.body.title;
     TodoModel.create({
        title,
        userId
     })
     res.json({
        userId: userId
     })

 });
 
 app.get("/todos", auth,  async function(req, res){
     const userId = req.userId;
     const todos = await TodoModel.find({
        userId: userId
     })
     res.json({
        todos
     })
 });

 function auth(req, res, next){
     const token = req.headers.token;
     const decodedData = jwt.verify(token, JWT_SECRET);

     if(decodedData){
        req.userId = decodedData.id;
        next();
     } else{
        res.status(403).json({
            message: "Incorrect Credentials"
        })
     }

 }
 

 app.listen(3000);

Todo application with mongodb as a database, jwt for authentication, zod for input validation and bcrypt for hashing the passwords to save to the DB.

index.js

javascript Copyconst bcrypt = require("bcrypt")
 const express =  require('express')
 const { UserModel, TodoModel } = require("./db");
 const jwt = require("jsonwebtoken");
 const { default: mongoose } = require('mongoose');
 const JWT_SECRET = "asdadslsg@123"
 const {z} = require("zod");

 mongoose.connect("mongodb+srv://titkaran09_db_user:WCFZpLejg1DhPUpN@cluster01.qc0er3j.mongodb.net/Todos")
 const app = express()

 app.use(express.json());

 app.post("/signup", async function(req, res){
      const requireBody = z.object({
        email: z.string().min(3).max(50).email(),
        name: z.string().min(3).max(50),
        password: z.string()
                   .min(8, "Password must be at least 8 characters long")
                   .max(30)
                   .regex(/[A-Z]/, "Password must contain at least one uppercase letter")
                   .regex(/[a-z]/, "Password must contain at least one lowercase letter")
                   .regex(/\d/, "Password must contain at least one number")
                   .regex(/[!@#$%^&*()_+\-=[\]{};':"\\|,.<>/?]/, "Password must contain at least one special character")
      })

      const parsedDataWithSuccess = requireBody.safeParse(req.body);

      if(!parsedDataWithSuccess.success){
        res.json({
            message: "Incorrect format",
            error: parsedDataWithSuccess.error

        })
        return
      }
      const email = req.body.email;
      const password = req.body.password;
      const name = req.body.name;
      let errorThrown = false;
      try{
           const hashedPassword = await bcrypt.hash(password, 5);
           console.log(hashedPassword)

            await UserModel.create({
                email: email,
                password: hashedPassword,
                name: name

      });
      } catch(e){
            res.json({
                message: "User already exists"
            })
            errorThrown = true;
      }

      if(!errorThrown){
        res.json({
        message: "You are signed up"
      })
      }
       
 });
 

app.post("/signin", async function (req, res) {
    
    const email = req.body.email;
    const password = req.body.password;
    

  
    const user = await UserModel.findOne({
        email: email,
    });
   
    
    if (!user) {
        return res.status(403).json({
            message: "Invalid Credentials!",
        });
    }

    // Compare the password with the hashed password using the bcrypt.compare() method
    const passwordMatch = await bcrypt.compare(password, user.password);

    // If the user password matches
    if (passwordMatch) {
        // Create a JWT token using the jwt.sign() method
        const token = jwt.sign({
                id: user._id.toString(),
            }, JWT_SECRET);
           

        // Send the token to the client
        res.json({
            token: token,
            message: "You are signed in!",
        });
    } else {
        
        res.status(403).json({
            message: "Invalid Credentials!",
        });
    }
});
 
 app.post("/todo", auth,  function(req, res){
     const userId = req.userId;
     const title = req.body.title;
     TodoModel.create({
        title,
        userId
     })
     res.json({
        userId: userId
     })

 });
 
 app.get("/todos", auth,  async function(req, res){
     const userId = req.userId;
     const todos = await TodoModel.find({
        userId: userId
     })
     res.json({
        todos
     })
 });

 function auth(req, res, next){
     const token = req.headers.token;
     const decodedData = jwt.verify(token, JWT_SECRET);

     if(decodedData){
        req.userId = decodedData.id;
        next();
     } else{
        res.status(403).json({
            message: "Incorrect Credentials"
        })
     }

 }
 

 app.listen(3000);

db.js

javascript Copyconst mongoose = require("mongoose")
const Schema = mongoose.Schema
const ObjectId = mongoose.ObjectId;

const User = new Schema({
    email: {type: String, unique: true},   
    password: String,
    name: String
})

const Todo = new Schema({
    title: String,
    done: Boolean,
    userId: ObjectId
})

const UserModel = mongoose.model('users', User)
const TodoModel = mongoose.model('todos', Todo)

module.exports= {
    UserModel: UserModel,
    TodoModel: TodoModel
}