1. Create an application in ReactJS to implement the component life cycle

Program:

// 1. Component Life Cycle (Class Component)
import React, { Component } from 'react';

class LifeCycleDemo extends Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
    console.log('Constructor called');
  }

  componentDidMount() {
    console.log('Component did mount');
  }

  componentDidUpdate() {
    console.log('Component did update');
  }

  componentWillUnmount() {
    console.log('Component will unmount');
  }

  incrementCount = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    console.log('Render method called');
    return (
      <div>
        <h1>Lifecycle Methods</h1>
        <p>Count: {this.state.count}</p>
        <button onClick={this.incrementCount}>Increment</button>
      </div>
    );
  }
}

export default LifeCycleDemo;

Explanation:

1. constructor():

   • When it runs: It runs once when the component is initialized (before it mounts to the DOM).

   • Console log: "Constructor called"

   • Purpose: To initialize state and bind event handlers.

2. render():

   • When it runs: It runs after the constructor and before componentDidMount. It also runs every time the state or props change.

   • Console log: "Render method called"

   • Purpose: To return the JSX (HTML) structure for the UI.

3. componentDidMount():

   • When it runs: It runs only once after the component is mounted to the DOM.

   • Console log: "Component did mount"

   • Purpose: To run side effects, API calls, subscriptions, and DOM manipulation after the component is mounted.

4. componentDidUpdate():

   • When it runs: It runs every time the state or props are updated and the component is re-rendered.

   • Console log: "Component did update"

   • Purpose: To run side effects after an update (like making API calls based on the updated data).

5. componentWillUnmount():

   • When it runs: It runs when the component is about to be removed from the DOM.

   • Console log: "Component will unmount"

   • Purpose: To clean up subscriptions, timers, or event listeners.

Example of the console log flow:

1. Component loads for the first time:

    Constructor called
    Render method called
    Component did mount
   

2. The user clicks the button to update the state:

    Render method called
    Component did update
   

The component is removed from the DOM:

Component will unmount

---

2. Create an application to implement class and functional components in ReactJS

Program:

//ClassComponent.jsx
import { Component } from "react";
class ClassComponent extends Component {
  render() {
    return <h1>This is a Class Component</h1>;
  }
}
export default ClassComponent;

import ClassComponent from "./ClassComponent.jsx";

const Functional = () => {
  return (
    <div>
      <ClassComponent />
      <h2>This is Functional Component</h2>
    </div>
  );
};

export default Functional;

import { createRoot } from "react-dom/client";
import Functional from "./Functional";

createRoot(document.getElementById("root")).render(<Functional />);

---

3. Create an application in ReactJS to import and export the files (components)

Program:

// File: Header.js
export const Header = () => {
  return (
    <header>
      <h1>Header Component</h1>
      <nav>
        <a href="/home">Home</a> | <a href="/about">About</a> | <a href="/contact">Contact</a>
      </nav>
    </header>
  );
};

// File: Footer.js
export const Footer = () => {
  return (
    <footer>
      <p>© 2024 Your Company</p>
    </footer>
  );
};

// File: App.js
import React from 'react';
import { Header } from './Header';
import { Footer } from './Footer';

function App() {
  return (
    <div>
      <Header />
      <main>
        <h1>Welcome to Our Website</h1>
        <p>This is the main content area.</p>
      </main>
      <Footer />
    </div>
  );
}

export default App;

---

4. Create an application to implement state and props

Program:

//ParentComponent.jsx
import  { useState } from "react";
import ChildComponent from "./ChildComponent";

const ParentComponent = () => {
  const [userName, setUserName] = useState("Vitthal");

  const changeUserName = () => {
    setUserName("Korvan");
  };

  return (
    <div>
      <h1>Welcome, {userName}!</h1>
      <ChildComponent name={userName} />
      <button onClick={changeUserName}>Change User Name</button>
    </div>
  );
};

export default ParentComponent;

//ChildComponent
const ChildComponent = ( { name } ) => {
  return <h2>Message is: Hello, {name}!</h2>;
};

export default ChildComponent;

//Main.jsx
import { createRoot } from "react-dom/client";
import ParentComponent from "./ParentComponent";

createRoot(document.getElementById("root")).render(<ParentComponent />);

---

5. Create an application in ReactJS to use DOM events

Program:

//App.jsx
import React from "react";

const App = () => {
  function handleClick() {
    alert("Button clicked!");
  }

  function handleInputChange(event) {
    console.log("Input value:", event.target.value);
  }

  function handleFocus() {
    console.log("Input focused");
  }

  return (
    <>
      <input type="text" onChange={handleInputChange} />
      <input type="text" onFocus={handleFocus} />
      <button onClick={handleClick}>Click Me</button>
    </>
  );
};

export default App;

//Main.jsx
import { StrictMode } from "react";
import { createRoot } from "react-dom/client";

import App from "./App.jsx";

createRoot(document.getElementById("root")).render(
  <StrictMode>
    <App />
  </StrictMode>
);

---

6. Create an application in ReactJS form and add client and server-side validation

Program:

//FormValidation.jsx
import { useState } from "react";

const FormValidation = () => {
  const [email, setEmail] = useState("");
  const [error, setError] = useState("");

  const validateEmail = (email) => {
    const regex = /^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$/g;
    return regex.test(email);
  };

  const handleSubmit = (e) => {
    e.preventDefault();
    if (!validateEmail(email)) {
      setError("Invalid email address");
    } else {
      setError("");
      alert("Form submitted successfully");
    }
  };

  return (
    <form onSubmit={handleSubmit}>
      <label>Email:</label>
      <input
        type="text"
        value={email}
        onChange={(e) => setEmail(e.target.value)}
      />
      {error && <p style={{ color: "red" }}>{error}</p>}
      <button type="submit">Submit</button>
    </form>
  );
};

export default FormValidation;

//Main.jsx
import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import FormValidation from './FormValidation.jsx'

createRoot(document.getElementById('root')).render(
  <StrictMode>
    <FormValidation />
  </StrictMode>,
)

---

7. Create an application to implement React Hooks

Program:

//HooksDemo.jsx
import { useState, useEffect } from "react";

const HooksDemo = () => {
  const [count, setCount] = useState(0);

  useEffect(() => {
    console.log("Component mounted or count updated");
    return () => {
      console.log("Cleanup on component unmount");
    };
  }, [count]);

  return (
    <div>
      <h1>Count: {count}</h1>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
};

export default HooksDemo;

//Main.jsx
import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import HooksDemo from './HooksDemo.jsx'

createRoot(document.getElementById('root')).render(
  <StrictMode>
    <HooksDemo />
  </StrictMode>,
)

---

8. Create SPA using React Router

npm install react-router-dom

Program:

//Home.jsx
const Home = () => {
  return (
    <div>
      <h1>Welcome to Home Page</h1>
      <p>This is the home page of our single-page application.</p>
    </div>
  );
};

export default Home;

//About.jsx
const About = () => {
  return (
    <div>
      <h1>Welcome to About Page</h1>
      <p>This is the About page of our single-page application.</p>
    </div>
  );
};

export default About;

//Contact.jsx
const Contact = () => {
  return (
    <div>
      <h1>Contact Us</h1>
      <p>Feel free to contact us via the form below.</p>
    </div>
  );
};

export default Contact;

//App.jsx
import { BrowserRouter as Router, Routes, Route, Link } from "react-router-dom";
import Home from "./components/Home";
import About from "./components/About";
import Contact from "./components/Contact";

const App = () => {
  return (
    <Router>
      <nav>
        <ul>
          <li>
            <Link to="/">Home</Link>
          </li>
          <li>
            <Link to="/about">About</Link>
          </li>
          <li>
            <Link to="/contact">Contact</Link>
          </li>
        </ul>
      </nav>

      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/about" element={<About />} />
        <Route path="/contact" element={<Contact />} />
      </Routes>
    </Router>
  );
};

export default App;

//Main.jsx

import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import App from './App.jsx'

createRoot(document.getElementById('root')).render(
  <StrictMode>
    <App />
  </StrictMode>,
)