Что то доделали. Надо сменить ветку

src/App.jsx

@@ -1,108 +1,96 @@
 import React from 'react'
+import styles from './App.module.scss'
 
-class MyComponent extends React.Component {
+class Clock extends React.Component {
     constructor(props) {
         super(props);
-        this.state = { data: null };
+        this.state = { date: new Date() };
-        this.handleClick = this.handleClick.bind(this);
     }
-    
-    render() {
-        return (
-            <div>
-            {this.state.data ? (
-                    <div>Данные: {this.state.data}</div>
-                ) : (
-                    <div>Загрузка...</div>
-                )}
-                <button onClick={this.handleClick}>Обновить</button>
-            </div>
-        )
-    }
-    
     componentDidMount() {
-        fetch('https://api.example.com/data')
+        this.timerId = setInterval( () => this.tick(), 1000);
-        .then(responce => responce.json())
-        .then(json => this.setState({data: json}));
-        
-        this.timerId = setInterval(()=> console.log('Tick'), 1000);
     }
-    
-    componentWillUnmout() {
-        clearInterval(this.timerId);
-    }
-    
-    handleClick() {
-        this.setState({data: 'Данные'})
-    }
-}
-
-class MyComponent2 extends React.Component {
-    controller = new AbortController()
-
-    componentDidMount() {
-        fetch('https://api.example.com/data',{ singnal: this.controller.signal })
-        .then(responce => responce.json())
-        .then(json => this.setState({data: json}))
-        .catch(error => {
-            if(error.name == 'AbortError') {
-                console.log('Aborted');
-            } else {
-                console.log('Other error',error);
-            }
-        });
-    }
-
     componentWillUnmount() {
-        this.controller.abort()
+        clearInterval(this.timerId)
+    }
+    tick() {
+        this.setState({ date: new Date() })
+    }
+    render() {
+        return <div>{this.state.date.toLocaleTimeString()}</div>
     }
 }
-class MyComponent3 extends React.Component {
+
-    componentDidMount() {
+function Clock2() {
-        this.loadData();
+    const [date, setDate] = React.useState(new Date());
+    
+    React.useEffect(()=>{
+        const timerId = setInterval(()=> setDate(new Date()),1000);
+        return () => clearInterval(timerId);
+    },[])
+    
+    return <div>{date.toLocaleTimeString()}</div>
+}
+
+function MouseTracker() {
+    const [x,setX] = React.useState(0);
+    const [y,setY] = React.useState(0);
+    
+    const mouseMoveHandler = event => {
+        setX(event.clientX);
+        setY(event.clientY);
     }
     
-    async loadData() {
+    React.useEffect(()=>{
-        try {
+        document.addEventListener('mousemove', mouseMoveHandler);
-            const response = await fetch('https://api.example.com/data');
+        return () => {
-            const data = await response.json();
+            document.removeEventListener('mousemove',mouseMoveHandler);
-            this.setSate({ data });
-        } catch {
-            console.log('error');
         }
-    }
+    },[]);
+    
+    return <div className={styles.container}>
+        <p>Координаты мыши:<br /> X:<b>{x}</b>, Y:<b>{y}</b></p>
+        </div>
 }
 
-class Timer extends React.Component {
+function DataFetcher() {
-    constructor(props) {
+    const [posts,setPosts] = React.useState([]);
-        super(props);
+    const [users,setUsers] = React.useState([]);
-        this.state = { seconds: 0 }
+    
+    const getPosts = async () => {
+        const response = await fetch('https://jsonplaceholder.typicode.com/posts');
+        const data = await response.json();
+        setUsers(data.reduce((acc, value) => {
+            if (!(value.userId in acc))
+                return [...acc,value.userId]
+            return acc
+        }))
+        console.log(users);
+        setPosts(data.slice(1,10));
+        
     }
     
-    componentDidMount() {
+    React.useEffect(() => {
-        console.log('Timer mounted');
+        console.log("Компонент создан");
-        this.interval = setInterval(()=>{
+        getPosts();
-            this.setState(prevState => ({seconds: prevState.seconds + 1}))
+        return () => {console.log("Компонент удален");setPosts([])};
-        },1000);
+    },[])
-    }
     
-    componentWillUnmount() {
+    return <div><ol>{posts.map(post => <li id={post.id}>{post.title}</li>)}</ol></div>
-        console.log('Timer unmount');
-        clearInterval(this.interval);
-    }
-    render() {
-        return <h2>Прошло секунд: {this.state.seconds}</h2>
-    }
 }
 
 function App() {
-    const [show,setShow] = React.useState(true);
+    const [tracker,setTracker] = React.useState(false);
+    const [dataFetcher,setDataFetcher] = React.useState(false);
     
 	return (
 		<>
-			<h1>Таймер с классом</h1>
+			<h1>Hello, React!</h1>
-            <button onClick={()=>setShow(prev => !prev)}>{show ? 'Скрыть' : 'Показать'} таймер</button>
+            <Clock />
-            {show && <Timer />}
+            <Clock2 />
+            <button onClick={() => setTracker(!tracker)}>Показать/Скрыть трекер</button>
+            { tracker && <MouseTracker /> }
+            <button onClick={() => setDataFetcher(!dataFetcher)}>Показать/Скрыть посты</button>
+            { dataFetcher && <DataFetcher /> }
 		</>
 	)
 }

src/App.module.scss

@@ -0,0 +1,11 @@
+.container {
+    width: 300px;
+    height: 200px;
+    border: 2px dashed grey;
+    margin: 10px;
+    text-align: center;
+    p {
+        margin-top: 20%;
+    }
+}
+

src/main.jsx

@@ -4,5 +4,7 @@ import { createRoot } from 'react-dom/client'
 import App from './App.jsx'
 
 createRoot(document.getElementById('root')).render(
+	<StrictMode>
 		<App />
+	</StrictMode>
 )