Что то доделали. Надо сменить ветку

src/App.jsx

@@ -1,59 +1,96 @@
-import { memo, useState, useMemo } from 'react'
+import React from 'react'
+import styles from './App.module.scss'
 
-function memoize(fn) {
-    const cache = new Map();
-    return function(...args) {
-        const key = JSON.stringify(args);
-        if (cache.has(key)) {
-            return cache.get(key);
+class Clock extends React.Component {
+    constructor(props) {
+        super(props);
+        this.state = { date: new Date() };
     }
-        const result = fn.apply(this, args);
-        cache.set(key,result);
-        return result;
+    componentDidMount() {
+        this.timerId = setInterval( () => this.tick(), 1000);
+    }
+    componentWillUnmount() {
+        clearInterval(this.timerId)
+    }
+    tick() {
+        this.setState({ date: new Date() })
+    }
+    render() {
+        return <div>{this.state.date.toLocaleTimeString()}</div>
     }
 }
 
-function fibonachi(n, memo={}) {
-    if (n in memo) {console.log(n);return memo[n];}
-    if (n <= 1) return 1;
-    memo[n] = fibonachi(n-1, memo) + fibonachi(n - 2, memo);
-    return memo[n];
+function Clock2() {
+    const [date, setDate] = React.useState(new Date());
+    
+    React.useEffect(()=>{
+        const timerId = setInterval(()=> setDate(new Date()),1000);
+        return () => clearInterval(timerId);
+    },[])
+    
+    return <div>{date.toLocaleTimeString()}</div>
 }
 
-const MyComponent = ({ value }) => {
-    console.log('Rendring');
-    return <div>{value}</div>
+function MouseTracker() {
+    const [x,setX] = React.useState(0);
+    const [y,setY] = React.useState(0);
+    
+    const mouseMoveHandler = event => {
+        setX(event.clientX);
+        setY(event.clientY);
+    }
+    
+    React.useEffect(()=>{
+        document.addEventListener('mousemove', mouseMoveHandler);
+        return () => {
+            document.removeEventListener('mousemove',mouseMoveHandler);
+        }
+    },[]);
+    
+    return <div className={styles.container}>
+        <p>Координаты мыши:<br /> X:<b>{x}</b>, Y:<b>{y}</b></p>
+        </div>
 }
 
-const MemoizedComponent = memo(MyComponent);
+function DataFetcher() {
+    const [posts,setPosts] = React.useState([]);
+    const [users,setUsers] = React.useState([]);
     
-const Child = memo(({ children }) => {
-    console.log('Child component rendred');
-    return <div>{children}</div>;
-});
+    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));
         
-const Parent = () => {
-    const [count,setCount] = useState(0);
-    const [text, setText] = useState('');
+    }
     
-    const stableChild = useMemo(() => <span>Memo text</span>,[]);
+    React.useEffect(() => {
+        console.log("Компонент создан");
+        getPosts();
+        return () => {console.log("Компонент удален");setPosts([])};
+    },[])
     
-    return (
-        <>
-            <Child>
-                {stableChild}
-            </Child>
-            <input type="text" onChange={(e) => setText(e.target.value)} value={text} />
-            <button onClick={() => setCount(count + 1)}>Increment {count}</button>
-        </>
-    )
+    return <div><ol>{posts.map(post => <li id={post.id}>{post.title}</li>)}</ol></div>
 }
 
 function App() {
+    const [tracker,setTracker] = React.useState(false);
+    const [dataFetcher,setDataFetcher] = React.useState(false);
+    
 	return (
 		<>
 			<h1>Hello, React!</h1>
-            <Parent />
+            <Clock />
+            <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>
 )