Что то доделали. Надо сменить ветку

src/App.jsx

@@ -1,44 +1,96 @@
-import { useMutation, QueryClientProvider, QueryClient } from '@tanstack/react-query'
+import React from 'react'
-import PostAddForm from './components/PostAddForm'
+import styles from './App.module.scss'
 
-/*
+class Clock extends React.Component {
-const mutation = useMutation({
+    constructor(props) {
-    mutationFn: newUser => {
+        super(props);
-        fetch('https://jsonplaceholder.typicode.com/users', {
+        this.state = { date: new Date() };
-            method: 'GET',
-            headers: {'Content-type':'application/json'},
-            body: JSON.stringify(newUser),
-        }).then(res => res.json())
     }
-})
+    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>
+    }
+}
 
-const createQueryClient = () => {
+function Clock2() {
-    new QueryClient({
+    const [date, setDate] = React.useState(new Date());
-        defaultOptions: {
+    
-            queries: {
+    React.useEffect(()=>{
-                staleTime: 5 * 60*1000,
+        const timerId = setInterval(()=> setDate(new Date()),1000);
-                retry: 1,
+        return () => clearInterval(timerId);
-                gcTime: 10*60*1000,
+    },[])
-                refetchOnWindowFocus: false,
+    
-            },
+    return <div>{date.toLocaleTimeString()}</div>
-            mutations: {
+}
-                retry:0,
+
-                onError: error => {console.error('Mutation error:',error.message)}
+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>
+}
+
+function DataFetcher() {
+    const [posts,setPosts] = React.useState([]);
+    const [users,setUsers] = React.useState([]);
+    
+    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));
+        
+    }
+    
+    React.useEffect(() => {
+        console.log("Компонент создан");
+        getPosts();
+        return () => {console.log("Компонент удален");setPosts([])};
+    },[])
+    
+    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 (
 		<>
-			{/* Добавьте тестовый контент для проверки */}
 			<h1>Hello, React!</h1>
-        <QueryClientProvider client={createQueryClient}>
+            <Clock />
-            <PostAddForm />
+            <Clock2 />
-        </QueryClientProvider>
+            <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%;
+    }
+}
+