Что то доделали. Надо сменить ветку

src/App.jsx

@@ -1,67 +1,97 @@
-import React, { useState, useReducer, useRef, memo } from 'react'
+import React from 'react'
+import styles from './App.module.scss'
 
-function tasksReducer(state, action) {
-    switch(action.type) {
-        case 'ADD_TASK':
-            return [...state, action.payload]
-        case 'TOGGLE_TASK':
-            return state.map(task => task.id === action.payload ? {...task, complite: !task.complite} : task)
-        case 'REMOVE_TASK':
-            return state.filter(task => task.id !== action.payload)
-        default:
-            return state
+class Clock extends React.Component {
+    constructor(props) {
+        super(props);
+        this.state = { date: new Date() };
+    }
+    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 TaskList = memo(function TaskList({tasks, onToggle, onRemove}) {
-    console.log("Rendred")
-    return (
-        <ul>
-        {tasks.map(({id, text, complite}) => (
-                <li key={id}
-                    style={{textDecoration: complite ? 'line-through' : 'none' }}>
-                    <input type="checkbox" checked={complite} onChange={()=>onToggle(id)} />
-                    {text}
-                    <button onClick={()=> onRemove(id)} style={{marginLeft: 10}}>
-                        Удалить
-                    </button>
-                </li>
-            ))}
-        </ul>
-    )
-})
+function Clock2() {
+    const [date, setDate] = React.useState(new Date());
     
-function App() {
-    const [tasks, dispatch] = useReducer(tasksReducer,[])
-    const [input,setInput] = useState('')
-    const [error,setError] = useState('')
-    const inputRef = useRef(null)
+    React.useEffect(()=>{
+        const timerId = setInterval(()=> setDate(new Date()),1000);
+        return () => clearInterval(timerId);
+    },[])
     
-    const addTask = () => {
-        if (input.trim() === '') {
-            setError('Пустой текст задачи')
-            return
-        }
-        setError('')
-        dispatch({
-            type: 'ADD_TASK',
-            payload: {id: Date.now(), text: input.trim(), complite: false }
-        })
-        setInput('')
-        inputRef.current.focus()
+    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);
     }
     
-	return (
-		<div style={{padding: 20}}>
-			<h1>Список дел</h1>
-			<input ref={inputRef} value={input} onChange={e => setInput(e.target.value)} />
-			<button onClick={addTask}>Добавить</button>
-            {error && <p style={{color: 'red'}}>{error}</p>}
+    React.useEffect(()=>{
+        document.addEventListener('mousemove', mouseMoveHandler);
+        return () => {
+            document.removeEventListener('mousemove',mouseMoveHandler);
+        }
+    },[]);
     
-            <TaskList tasks={tasks} 
-                onToggle={id => dispatch({type: 'TOGGLE_TASK', payload: id})}
-                onRemove={id => dispatch({type: 'REMOVE_TASK', payload: id})} />
-		</div>
+    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 (
+		<>
+			<h1>Hello, React!</h1>
+            <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%;
+    }
+}
+