React Modernization

// Before: Class component
class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0,
      name: "",
    };
  }

// Before: Lifecycle methods
class DataFetcher extends React.Component {
  state = { data: null, loading: true };

  componentDidMount() {
    this.fetchData

// Before: Context consumer and HOC
const ThemeContext = React.createContext();

class ThemedButton extends React.Component {
  static contextType = ThemeContext;

  render() {
    return (

// Before: React 17
import ReactDOM from "react-dom";

ReactDOM.render(<App />, document.getElementById("root"));

// After: React 18
import { createRoot } from "react-dom/client";

const root = createRoot(document.getElementById("root"));
root.render(<

// React 18: All updates are batched
function handleClick() {
  setCount((c) => c + 1);
  setFlag((f) => !f);
  // Only one re-render (batched)
}

// Even in async:
setTimeout(() => {
  setCount((c) 

import { useState, useTransition } from "react";

function SearchResults() {
  const [query, setQuery] = useState("");
  const [results, setResults] = useState([]);
  const [isPending

import { Suspense } from "react";

// Resource-based data fetching (with React 18)
const resource = fetchProfileData();

function ProfilePage() {
  return (
    <Suspense fallback={<Loading />}>
      <ProfileDetails />