ReactJS is used to build single-page applications, mobile apps, and desktop apps.
It is used to build reusable UI components.

A component is a small, reusable piece of code that is responsible for one job.
It is used to split the UI into independent, reusable pieces, and think about each piece in isolation.

The virtual DOM (VDOM) is a programming concept where an ideal, or “virtual”, representation of a UI is kept in memory and synced with the “real” DOM by a library such as ReactDOM.
This process is called reconciliation.

Data is passed between components in ReactJS using props. Props are arguments passed into React components.
Props are passed to components via HTML attributes.

<ChildComponent name="John Doe" />;

In the above example, the `name` prop is passed to the `ChildComponent` component. The `ChildComponent` component can access the `name` prop using `props.name` or you can directly destructure the `name` prop from the props object.

JSX (JavaScript XML) is a syntax extension for JavaScript that allows developers to write HTML-like code in their JavaScript files.
It is used in conjunction with React, a JavaScript library for building user interfaces, to define the UI components of an app.

const element = <h1>Hello, world!</h1>;

The main difference between a class component and a functional component in ReactJS are as follows:

Here is Example of Class Component:

import React, { Component } from "react";

class MyComponent extends Component {
  render() {
    return <p>Hello, world!</p>;
  }
}

Here is Example of Functional Component:

import React from "react";

function MyComponent() {
  return <p>Hello, world!</p>;
}

Events are handled in ReactJS using event handlers. Event handlers are functions that are called when an event occurs.
Event handlers are passed as attributes to the elements that we want to handle events on.

<button onClick={handleClick}>Click Me</button>;

Synthetic events are cross-browser wrapper around the browser’s native event. They work identically across all browsers.
Synthetic events are pooled, which means that the synthetic event object will be reused and all properties will be nullified after the event callback has been invoked. This is for performance reasons.
To access the event properties in an asynchronous way, you should call event.persist() on the event, which will remove the event from the synthetic event pool and allow references to the event to be retained by user code.

import React from "react";

function MyComponent() {
  function handleClick(e) {
    e.preventDefault();
    console.log("The link was clicked.");
  }

  return (
    <a href="#" onClick={handleClick}>
      Click me
    </a>
  );
}

Components are styled in ReactJS using inline styles, CSS stylesheets, and CSS-in-JS.

Inline Styles:

<div style={{ color: "red" }}></div>;

CSS Stylesheets:

import "./styles.css";

CSS-in-JS:

import styled from "styled-components";

The ReactJS lifecycle refers to the series of methods that are called in different stages of the component’s existence.
These methods are called in a specific order during the mounting and updating of a component.

Server-side rendering is performed in ReactJS using the ReactDOMServer module.
The ReactDOMServer module is used to render React components to static markup.

PropTypes module is used to check the type of props passed to a component.
It is used to ensure that the props passed to a component are of the correct type.

import PropTypes from "prop-types";

MyComponent.propTypes = {
  name: PropTypes.string.isRequired,
};

If someone uses the `MyComponent` component and passes it a prop called `name` that is not a string, then PropTypes will log a warning in the developer console.

Context API is used to pass data through the component tree without having to pass props down manually at every level.
Context API is used to share data that can be considered “global” for a tree of React components.

import React, { createContext, useContext } from "react";

const MyContext = createContext();

//create a provider
<MyContext.Provider value={"hello world!"}>
  <ChildComponent />
</MyContext.Provider>;

//use the context
const ChildComponent = () => {
  const value = useContext(MyContext);
  return <div>{value}</div>;
};

Router is a library that is used to manage navigation in a single-page app.
It is used to define the routes of an app and to render the appropriate components when a route is matched.

import { BrowserRouter as Router, Route, Link, Switch } from "react-router-dom";

const Home = () => <h1>Home</h1>;
const About = () => <h1>About</h1>;
const NotFound = () => <h1>404: Not found</h1>;

const App = () => (
  <Router>
    <Switch>
      <Route exact path="/" component={Home} />
      <Route exact path="/about" component={About} />
      <Route component={NotFound} />
    </Switch>
  </Router>
);

The `BrowserRouter` component is used to define the routes of the app. The `Route` component is used to define the path of a route and the component that should be rendered when the route is matched. The `Switch` component is used to render the first route that matches the current URL.

A ReactJS app is tested using the Jest testing framework.
Jest is a JavaScript testing framework that is used to test React apps.

import React from "react";
import { render } from "@testing-library/react";
import App from "./App";

test("renders learn react link", () => {
  const { getByText } = render(<App />);
  const linkElement = getByText(/learn react/i);
  expect(linkElement).toBeInTheDocument();
});

The ReactJS Reconciliation algorithm is a process that is used to update the DOM when a component’s props or state changes.
It is used to update the DOM in an efficient way by minimizing the number of DOM operations.

JSX (JavaScript XML) is a syntax extension for JavaScript that allows developers to write HTML-like code in their JavaScript files.
It is used in conjunction with React, a JavaScript library for building user interfaces, to define the UI components of an app.

return (
  <div className="App">
    <h1>Hello World</h1>
    <button>Click Me</button>
  </div>
);

No, web browsers cannot read JSX directly.
JSX is a syntax extension for JavaScript and is not a valid JavaScript code.
JSX code is compiled to JavaScript code using a tool called Babel.

The key attribute is used to give a unique identifier to each element in a list.
It is used by React to identify which items have changed, are added, or are removed.

Keys are used by React to determine which elements in a list have changed, added, or been removed.
When an element is added or removed, React uses the key to determine which element has changed, and re-renders the appropriate components.
If you use the index of an element as the key, React will have to re-render all elements in the list whenever the list changes, because the index of every element will have changed.

ES5 is the fifth edition of the ECMAScript standard.
It was standardized in 2009 and is the most widely used version of JavaScript.
ES5 is supported by all modern browsers.

ES6 is the sixth edition of the ECMAScript standard.
It was standardized in 2015.

// 1. Require VS Import

// ES5
var React = require("react");
var ReactDOM = require("react-dom");

// ES6
import React from "react";
import ReactDOM from "react-dom";

// 2. exports VS export

// ES5
module.exports = MyComponent;

// ES6
export default MyComponent;

The useState Hook is used to manage the state of a component.
It is used to store the state of a component and to update the state of a component.

The useReducer Hook is used to manage the state of a component in a more complex way.
It is used to store the state of a component and to update the state of a component in a more complex way.

here is an example of the useState Hook:

import React, { useState } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
}

here is an example of the useReducer Hook:

import React, { useReducer } from "react";

const initialState = { count: 0 };

function reducer(state, action) {
  switch (action.type) {
    case "increment":
      return { count: state.count + 1 };
    case "decrement":
      return { count: state.count - 1 };

    default:
      throw new Error();
  }
}

function Counter() {
  const [state, dispatch] = useReducer(reducer, initialState);
  return (
    <>
      Count: {state.count}
      <button onClick={() => dispatch({ type: "decrement" })}>-</button>
      <button onClick={() => dispatch({ type: "increment" })}>+</button>
    </>
  );
}

The useEffect Hook is used to perform side effects in a function component.
It is used to perform side effects such as fetching data from an API, setting up a subscription, or manually changing the DOM in React components.

import React, { useState, useEffect } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    document.title = `You clicked ${count} times`;
  });

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
}

These are the main differences between ReactJS and AngularJS:

The useState Hook is used to manage the state of a component.
It is used to store the state of a component and to update the state of a component.

here is an example of the useState Hook:

import React, { useState } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
}

The useEffect Hook is used to perform side effects in a function component.
It is used to perform side effects such as fetching data from an API, setting up a subscription, or manually changing the DOM in React components.

import React, { useState, useEffect } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    document.title = `You clicked ${count} times`;
  });

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
}

In React, useRef() is a hook that allows you to create a reference to a DOM element or a component instance. It can be used to access and manipulate the element or component after it has been rendered.

The useRef Hook is used to create a reference to a DOM element.
It is used to access the DOM nodes directly.

For example, you can use useRef() to create a reference to a text input element, and then use the current property to access the value of the input or focus the input.

import React, { useRef } from "react";

function MyComponent() {
  const inputRef = useRef(null);

  function handleClick() {
    inputRef.current.focus();
  }

  return (
    <div>
      <input type="text" ref={inputRef} />
      <button onClick={handleClick}>Focus the input</button>
    </div>
  );
}

The useContext Hook is used to access the context value from a context object.
It is used to access the context value from a context object created by the React.createContext() method.

For example, you can use useContext() to access the context value from a context object created by the React.createContext() method.

import React, { useContext } from "react";

const MyContext = React.createContext();

function MyComponent() {
  const value = useContext(MyContext);
  return <div>{value}</div>;
}

function App() {
  return (
    <MyContext.Provider value={42}>
      <MyComponent />
    </MyContext.Provider>
  );
}

The useReducer Hook is used to manage the state of a component in a more complex way.
It is used to store the state of a component and to update the state of a component in a more complex way.

here is an example of the useReducer Hook:

import React, { useReducer } from "react";

const initialState = { count: 0 };

function reducer(state, action) {
  switch (action.type) {
    case "increment":
      return { count: state.count + 1 };
    case "decrement":
      return { count: state.count - 1 };

    default:
      throw new Error();
  }
}

function Counter() {
  const [state, dispatch] = useReducer(reducer, initialState);
  return (
    <>
      Count: {state.count}
      <button onClick={() => dispatch({ type: "decrement" })}>-</button>
      <button onClick={() => dispatch({ type: "increment" })}>+</button>
    </>
  );
}

The useCallback Hook is used to return a memoized callback. It is used to return a memoized callback.

useCallback will return a memoized version of the callback that only changes if one of the dependencies has changed. This is useful when passing callbacks to optimized child components that rely on reference equality to prevent unnecessary renders (e.g. shouldComponentUpdate).

here is an example of the useCallback Hook:

import React, { useState, useCallback } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);

  const increment = useCallback(() => {
    setCount(count + 1);
  }, [count]);

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={increment}>Increment count</button>
    </div>
  );
}

The useMemo Hook is used to return a memoized value. It is used to return a memoized value.

useMemo will only recompute the memoized value when one of the dependencies has changed. This optimization helps to avoid expensive calculations on every render.

here is an example of the useMemo Hook:

import React, { useState, useMemo } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);
  const [count2, setCount2] = useState(0);

  const expensiveValue = useMemo(() => {
    return count * 2;
  }, [count]);

  return (
    <div>
      <p>Count: {count}</p>
      <p>Count2: {count2}</p>
      <p>Expensive Value: {expensiveValue}</p>
      <button onClick={() => setCount(count + 1)}>Increment count</button>
      <button onClick={() => setCount2(count2 + 1)}>Increment count2</button>
    </div>
  );
}

1. ReactJS uses Virtual DOM instead of Real DOM.
2. React can be rendered on the server as well as the client, which can improve the performance and SEO of the app.
3. ReactJS follows uni-directional data flow or data binding.This makes it easier to understand and debug the app, as the flow of data is predictable and explicit.
4. ReactJS uses reusable/composable UI components to develop the view.
5. ReactJS uses JSX as its primary scripting language.This allows developers to write HTML-like code in their JavaScript files, making it easier to build and style UI components.
6. ReactJS uses one-way data binding between the components.
7. ReactJS uses Flux architecture.

The main difference between Virtual DOM and Real DOM are as follows:

The main difference between Stateful and Stateless components are as

There are many ways to pass data between different components in React: -

1. Props - Props are used to pass data from one component to another. Props are immutable and are passed from parent to child components.
   

   function ParentComponent() {
     const [name, setName] = useState("hello");
     return <ChildComponent name={name} />;
   }
   
   function ChildComponent(props) {
     return <div>{props.name}</div>;
   }
   

2. Context - Context is used to pass data through the component tree without having to pass props down manually at every level.
   

   const CustomContext = React.createContext();
   const [name, setName] = useState("hello");
   function ParentComponent() {
     return (
       <CustomContext.Provider value={{ name }}>
         <ChildComponent />
       </CustomContext.Provider>
     );
   }
   
   function ChildComponent() {
     return (
       <CustomContext.Consumer>
         {(context) => <div>{context.name}</div>}
       </CustomContext.Consumer>
     );
   }
   

3. Redux - Redux is a predictable state container for JavaScript apps. It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test. On top of that, it provides a great developer experience, such as live code editing combined with a time traveling debugger.
   

   import { connect } from "react-redux";
   
   function mapStateToProps(state) {
     return {
       name: state.name,
     };
   }
   
   function ChildComponent(props) {
     return <div>{props.name}</div>;
   }
   
   export default connect(mapStateToProps)(ChildComponent);
   

To implement routing in a React application, you can use the react-router-dom library. This library provides a `Router` component that manages the application's routing, and a set of `Route` components that define the individual routes in your application.

import { BrowserRouter as Router, Route, Link, Routes } from "react-router-dom";

function App() {
  return (
    <Router>
      <Routes>
        <Route exact path="/" component={Home} />
        <Route path="/about" component={About} />
        <Route path="/topics" component={Topics} />
      </Routes>
    </Router>
  );
}

A higher-order component (HOC) is an advanced technique in React for reusing component logic. HOCs are not part of the React API, per se. They are a pattern that emerges from React’s compositional nature.

const MyComponent = (props) => {
  return <div>{props.name}</div>;
};

export default withMyHOC(MyComponent);

The main advantage of using HOC in React are as follows:

There are many ways to modularize your React application. Here are a few ways to do it:

1. Components - Components are the building blocks of a React application. They are the smallest units of code that can be reused in a React application. Components are the building blocks of a React application. They are the smallest units of code that can be reused in a React application.
   
2. Containers - Containers are components that are connected to the Redux store. They are responsible for fetching data from the store and passing it to the presentational components.
   
3. Presentational Components - Presentational components are components that are responsible for displaying data. They are typically stateless components that receive data and callbacks exclusively via props.
   

In React, you can handle forms in a number of ways. Here is one way to do it:

1. Create a form element in your render method with an onSubmit event handler:

   return <form onSubmit={handleSubmit}>{/* form fields */}</form>;
   

2. Define the `handleSubmit` method in your component class. This method will be called when the form is submitted.

   handleSubmit = (event) => {
     event.preventDefault();
     const { name, email, password } = event.target;
   };
   

3. You can also use controlled components to manage the state of the form fields. In this case, you will need to store the form data in the component's state, and update the state whenever the form fields change.

   function Login() {
     const [userData, setUserData] = useState({
       email: "",
       password: "",
     });
   
     const handleChange = (event) => {
       const { name, value } = event.target;
       setUserData({ ...userData, [name]: value });
     };
   
     const handleSubmit = (event) => {
       event.preventDefault();
       const { email, password } = userData;
       console.log(email, password);
     };
   
     return (
       <form onSubmit={handleSubmit}>
         <input
           type="email"
           name="email"
           value={userData.email}
           onChange={handleChange}
         />
         <input
           type="password"
           name="password"
           value={userData.password}
           onChange={handleChange}
         />
         <button type="submit">Login</button>
       </form>
     );
   }
   

There are many ways to optimize the performance of a React application. Here are some of them:

1. Use the `React.memo` higher-order component to wrap functional components that do not need to re-render when their props don't change. This can prevent unnecessary re-renders and improve performance.
2. Use the `React.useCallback` hook to memoize callback functions. This can prevent unnecessary re-creating of functions on every render, improving performance.
3. Use the `React.useRef` hook to store mutable values that do not need to trigger a re-render when they change. This can prevent unnecessary re-renders caused by updates to these values.
4. Use the `React.useReducer` hook instead of the React.useState hook when you have complex state logic that involves multiple state variables or asynchronous updates. This can improve the performance of your application by avoiding unnecessary re-renders.
5. Use the `React.lazy` and `React.Suspense` components to implement code splitting and lazy loading in your application. This can improve the performance of your application by only loading the code that is needed for a particular route or component.

Here is an example of how to set up Jest and write a simple unit test for a React component:

1. Install the Jest testing framework and the React testing library:

   npm install --save-dev jest;
   

2. Create a test file in your project. The test file should have the same name as the component file, but with the .test.js extension. For example, if you have a component in a file called Button.js, you should create a test file called Button.test.js.
   
3. Write a test for your component. For example, you can check that element present in the component renders correctly.

   test("MyComponent should render the correct content", () => {
     const { getByText } = render(<MyComponent />);
     const element = getByText(/Hello, world!/i);
     expect(element).toBeInTheDocument();
   });
   

Higher-order components are functions that take a component as an argument and return a new component.
They can be used to add functionality to a component, such as adding a new prop or state value, or adding a new method.

const withLoading = (Component) => {
  return function WihLoadingComponent({ isLoading, ...props }) {
    if (!isLoading) return <Component {...props} />;
    return <p>Hold on, fetching data may take some time.</p>;
  };
};

const App = ({ isLoading }) => {
  return (
    <div>
      <h1>My App</h1>
      <p>App is running</p>
    </div>
  );
};

const AppWithLoading = withLoading(App);

const App = () => {
  return (
    <div>
      <AppWithLoading isLoading={true} />
    </div>
  );
};

The React Suspense and lazy APIs can be used to implement code splitting and lazy loading in a React application.
Here is an example of how to use them:

import React, { Suspense, lazy } from "react";

const OtherComponent = lazy(() => import("./OtherComponent"));

function MyComponent() {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <OtherComponent />
    </Suspense>
  );
}

The React ref API can be used to access the DOM.
You can use the ref prop to pass a callback function to a component. This callback function will be called with the DOM element as an argument when the component mounts.
You can then store the DOM element in a variable and use it to access the DOM.

Here is an example of how to use it:

import React, { useRef } from "react";

function MyComponent() {
  const inputRef = useRef(null);

  function handleClick() {
    inputRef.current.focus();
  }

  return (
    <div>
      <input type="text" ref={inputRef} />
      <button onClick={handleClick}>Focus the input</button>
    </div>
  );
}

The React memo API can be used to optimize functional components.
You can use the React.memo higher-order component to wrap a functional component.
This will prevent the component from re-rendering when its props do not change.
This can improve the performance of your application.

Here is an example of how to use it:

import React, { useState, memo } from "react";

const MyComponent = memo(function MyComponent(props) {
  /* only rerenders if props change */
});

There are three types of hooks provided by React:

1. State hooks - These hooks can be used to add state to a functional component.
   The `useState` hook can be used to add a state variable to a functional component.
   The `useReducer` hook can be used to add a state variable that is managed by a reducer function.
   The `useContext `hook can be used to add a state variable that is managed by a context object.
   
2. Effect hooks - These hooks can be used to add side effects to a functional component.
   The `useEffect` hook can be used to add a side effect to a functional component.
   The `useLayoutEffect` hook can be used to add a side effect to a functional component that is executed after the DOM is updated.
   
3. Other hooks - These hooks can be used to add other functionality to a functional component.
   The `useRef` hook can be used to add a mutable ref object to a functional component.
   The `useImperativeHandle` hook can be used to add a custom method to a functional component.
   The `useMemo` hook can be used to add a memoized value to a functional component.
   The `useCallback` hook can be used to add a memoized callback function to a functional component.
   The `useDebugValue ` hook can be used to add a custom label to a functional component in the React DevTools.
   

Pure components are components that do not re-render when their props do not change.
They can be used to improve the performance of your application.
You can create a pure component by extending the React.PureComponent class.
You can also create a pure component by using the React.memo higher-order component.

Here is an example of how to use it:

import React, { PureComponent } from "react";

class MyComponent extends PureComponent {
  render() {
    return <div>{this.props.name}</div>;
  }
}

The virtual DOM is a copy of the actual DOM. It is a lightweight representation of the actual DOM.
It is a JavaScript object that is kept in memory. It is synced with the actual DOM by a library such as ReactDOM. This process is called reconciliation.
The virtual DOM is faster than the actual DOM because it is a lightweight representation of the actual DOM.
It is faster because it does not need to be updated as often as the actual DOM. It is updated only when there is a change in the state of the application.

In a React application, you can handle asynchronous actions, such as API calls, in a few different ways. One common approach is to use the `async` and `await` keywords, which are part of the JavaScript language and allow you to write asynchronous code that looks and behaves like synchronous code.
There are many other ways to handle asynchronous actions in a React application, such as using the Promise API or the async and await keywords with the fetch function. Ultimately, the choice of which approach to use will depend on your specific needs and preferences.

import React, { useState, useEffect } from "react";

function Component() {
  const [data, setData] = useState(null);

  useEffect(() => {
    async function fetchData() {
      const response = await fetch("your api url");
      const data = await response.json();
      setData(data);
    }
    fetchData();
  }, []);

  return <div>{data ? <p>{data.message}</p> : <p>Loading...</p>}</div>;
}

In the above example, we are using the `async` and `await` keywords to handle asynchronous actions in a React application. We are using the `async` keyword to define an asynchronous function, and we are using the `await` keyword to wait for the asynchronous function to complete before continuing with the rest of the code.

Another common way to handle asynchronous actions in a React application is to use a library like axios to make HTTP requests. For example:

import React, { useState, useEffect } from "react";
import axios from "axios";

function MyComponent() {
  const [data, setData] = useState(null);

  useEffect(() => {
    async function fetchData() {
      const response = await axios.get("https://my-api.com/endpoint");
      setData(response.data);
    }
    fetchData();
  }, []);

  return <div>{data ? <p>{data.message}</p> : <p>Loading...</p>}</div>;
}

A controlled form element is an element whose value is controlled by React. For example, a controlled input element would have its value controlled by React, and would not update its value based on user input.
An uncontrolled form element is an element whose value is not controlled by React. For example, an uncontrolled input element would have its value controlled by the user, and would not update its value based on React state.

Here's an example of a controlled form element in a React component:

import React, { useState } from "react";

function MyForm() {
  const [email, setEmail] = useState("");

  function handleChange(event) {
    setEmail(event.target.value);
  }

  return (
    <form>
      <label htmlFor="email">Email:</label>
      <input type="text" id="email" value={email} onChange={handleChange} />
    </form>
  );
}

There are many ways to optimize the performance of a React application. Some of the most common techniques include:

1. Using the `React.lazy` and `React.Suspense` components to implement code-splitting and lazy-loading of components.
2. Using the `PureComponent` class to prevent unnecessary re-renders.
3. Using the `React.memo` higher-order component to memoize functional components and avoid unnecessary re-renders.
4. Using the `useMemo` hook to prevent unnecessary re-renders.
5. Using the `useCallback` hook to prevent unnecessary re-renders.
6. Using the `key` prop when rendering a list of elements to help React identify which elements have changed and avoid unnecessary re-renders.

Here's an example of using `useMemo` to prevent unnecessary re-renders:

import React, { useState, useMemo } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);

  const expensiveValue = useMemo(() => {
    // do something expensive
    return count * 2;
  }, [count]);

  return (
    <div>
      <p>{expensiveValue}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

Here's an example of using `useCallback` to prevent unnecessary re-renders:

import { useCallback } from "react";

function MyComponent(props) {
  const handleClick = useCallback(() => {
    console.log(props.a);
  }, [props.a]);

  return <MyChildComponent onClick={handleClick} />;
}

An Error Boundary is a component that can catch JavaScript errors anywhere in its child component tree, log those errors, and display a fallback UI instead of the component tree that crashed.
Error boundaries catch errors during rendering, in lifecycle methods, and in constructors of the whole tree below them.

Here's an example of using an Error Boundary component to handle errors in a React application:

import React, { Component } from "react";

class ErrorBoundary extends Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }

  static getDerivedStateFromError(error) {
    // Update state so the next render will show the fallback UI.
    return { hasError: true };
  }

  componentDidCatch(error, errorInfo) {
    // You can also log the error to an error reporting service
    logErrorToMyService(error, errorInfo);
  }

  render() {
    if (this.state.hasError) {
      // You can render any custom fallback UI
      return <h1>Something went wrong.</h1>;
    }

    return this.props.children;
  }
}

There are a few ways to achieve lifecycle methods in functional components. Some of the most common techniques include:

1. Using the `useEffect` hook to implement the `componentDidMount`, `componentDidUpdate`, and `componentWillUnmount` lifecycle methods.
2. Using the `useLayoutEffect` hook to implement the `componentDidMount` and `componentDidUpdate` lifecycle methods.

Here's an example of using the `useEffect` hook to implement the `componentDidMount` , `componentDidUpdate`, and `componentWillUnmount` lifecycle methods:

import React, { useState, useEffect } from "react";

function MyComponent() {
  const [count, setCount] = useState(0);

  // componentDidMount using useEffect
  useEffect(() => {
    // do something
  }, []);

  // componentDidUpdate using useEffect
  useEffect(() => {
    // do something
  }, [count]);

  // componentWillUnmount using useEffect
  useEffect(() => {
    return () => {
      // do something
    };
  }, []);

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click me</button>
    </div>
  );
}

Here's an example of a countdown timer built using ReactJs:

Here's an example of a React Project with Optimize search filter in ReactJs using debounce and infinite scroll(Pagination):

Here's an example of a React counter application with start, reset, and pause functionality:

First of all, if you know all of the above, what are you doing here dude!
You should be working on your own projects.

OtherWise you can check out these projects to get started with ReactJs: