1. Setting Up the Backend

mkdir mern-todo-app
cd mern-todo-app
npm init -y

1.2. Install Dependencies

`npm install express mongoose body-parser cors
`

1.3. Set Up the Server
Create an index.js file to set up the Express server and connect to MongoDB.

// index.js
const express = require('express');
const mongoose = require('mongoose');
const bodyParser = require('body-parser');
const cors = require('cors');

const app = express();
const PORT = process.env.PORT || 5000;

mongoose.connect('mongodb://localhost:27017/todoapp', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', () => {
  console.log('Connected to MongoDB');
});

app.use(bodyParser.json());
app.use(cors());

app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

1.4. Create Mongoose Models
Create a models directory and define the Todo model.

// models/Todo.js
const mongoose = require('mongoose');

const todoSchema = new mongoose.Schema({
  text: { type: String, required: true },
  completed: { type: Boolean, default: false },
  createdAt: { type: Date, default: Date.now },
});

const Todo = mongoose.model('Todo', todoSchema);

module.exports = Todo;

1.5. Create Routes
Create a routes directory and define the routes for the CRUD operations

// routes/todoRoutes.js
const express = require('express');
const Todo = require('../models/Todo');

const router = express.Router();

// Create a new todo
router.post('/', async (req, res) => {
  try {
    const todo = new Todo({
      text: req.body.text,
    });
    await todo.save();
    res.status(201).json(todo);
  } catch (err) {
    res.status(400).json({ error: err.message });
  }
});

// Get all todos
router.get('/', async (req, res) => {
  try {
    const todos = await Todo.find();
    res.status(200).json(todos);
  } catch (err) {
    res.status(400).json({ error: err.message });
  }
});

// Update a todo
router.put('/:id', async (req, res) => {
  try {
    const todo = await Todo.findByIdAndUpdate(req.params.id, req.body, { new: true });
    res.status(200).json(todo);
  } catch (err) {
    res.status(400).json({ error: err.message });
  }
});

// Delete a todo
router.delete('/:id', async (req, res) => {
  try {
    await Todo.findByIdAndDelete(req.params.id);
    res.status(200).json({ message: 'Todo deleted successfully' });
  } catch (err) {
    res.status(400).json({ error: err.message });
  }
});

module.exports = router;

Integrate the routes into the index.js file.

// index.js const todoRoutes = require('./routes/todoRoutes'); app.use('/api/todos', todoRoutes);

2. Setting Up the Frontend

2.1. Initialize the React Project
Create a new React project using Create React App.

npx create-react-app client
cd client

2.2. Install Dependencies
Install Axios for making HTTP requests.

npm install axios

2.3. Create Components
Create a components directory and add the following components: TodoList, TodoItem, and TodoForm.

TodoList Component

// src/components/TodoList.js
import React, { useEffect, useState } from 'react';
import axios from 'axios';
import TodoItem from './TodoItem';
import TodoForm from './TodoForm';

const TodoList = () => {
  const [todos, setTodos] = useState([]);

  useEffect(() => {
    fetchTodos();
  }, []);

  const fetchTodos = async () => {
    const response = await axios.get('http://localhost:5000/api/todos');
    setTodos(response.data);
  };

  const addTodo = async (text) => {
    const response = await axios.post('http://localhost:5000/api/todos', { text });
    setTodos([...todos, response.data]);
  };

  const updateTodo = async (id, updatedTodo) => {
    const response = await axios.put(`http://localhost:5000/api/todos/${id}`, updatedTodo);
    setTodos(todos.map(todo => (todo._id === id ? response.data : todo)));
  };

  const deleteTodo = async (id) => {
    await axios.delete(`http://localhost:5000/api/todos/${id}`);
    setTodos(todos.filter(todo => todo._id !== id));
  };

  return (
    <div>
      <h1>Todo List</h1>
      <TodoForm addTodo={addTodo} />
      {todos.map(todo => (
        <TodoItem
          key={todo._id}
          todo={todo}
          updateTodo={updateTodo}
          deleteTodo={deleteTodo}
        />
      ))}
    </div>
  );
};

export default TodoList;

TodoItem Component

// src/components/TodoItem.js
import React from 'react';

const TodoItem = ({ todo, updateTodo, deleteTodo }) => {
  const toggleComplete = () => {
    updateTodo(todo._id, { ...todo, completed: !todo.completed });
  };

  return (
    <div>
      <input
        type="checkbox"
        checked={todo.completed}
        onChange={toggleComplete}
      />
      <span style={{ textDecoration: todo.completed ? 'line-through' : 'none' }}>
        {todo.text}
      </span>
      <button onClick={() => deleteTodo(todo._id)}>Delete</button>
    </div>
  );
};

export default TodoItem;

TodoFormComponent

// src/components/TodoForm.js
import React, { useState } from 'react';

const TodoForm = ({ addTodo }) => {
  const [text, setText] = useState('');

  const handleSubmit = (e) => {
    e.preventDefault();
    addTodo(text);
    setText('');
  };

  return (
    <form onSubmit={handleSubmit}>
      <input
        type="text"
        value={text}
        onChange={(e) => setText(e.target.value)}
        placeholder="Add a new todo"
      />
      <button type="submit">Add</button>
    </form>
  );
};

export default TodoForm;

2.4. Integrate Components in App
Update the App.js file to include the TodoList component.

// src/App.js
import React from 'react';
import TodoList from './components/TodoList';

function App() {
  return (
    <div className="App">
      <TodoList />
    </div>
  );
}

export default App;

2.5. Run the Application
Start the backend server and the React frontend.

`# In the root directory
node index.js

In the client directory

npm start
`

crud in mern stack

1. Setting Up the Backend

2. Setting Up the Frontend

In the client directory