final

src/App.jsx

@@ -1,98 +1,45 @@
-import { useState, useRef, useEffect } from 'react'
+import React, { useMemo, useCallback, useState } from 'react'
 
-function Example() {
-    const myRef = useRef(null);
-    const counterRef = useRef(0);
-    const [text, setText] = useState('');
+const TodoItem = React.memo(({ item, onToggle, onDelete }) => {
+    console.log(`rendred ${item.id}`);
+    return <li>
+            {item.name}
+            <button onClick={() => onToggle(item.id)}>Done</button>
+            <button onClick={() => onDelete(item.id)}>remove</button>
+        </li>
+})
 
-    useEffect(() => {
-        myRef.current?.focus();
+function ItemList({ items }) {
+
+    const handleToggle = useCallback(id => {
+        items.done = true;
+        console.log(`Item ${id} done`)
+        console.log(id)
     },[]);
     
-    const handlerFocus = () => {
-        if(myRef.current) {
-            myRef.current.focus();
-        }
-    };
-    
-    const handlerChange = (event) => {
-        setText(event.target.value);
-    }
-    counterRef.current += 1;
-    return <div>
-        <input ref={myRef} text="text" /><br />
-        Количество рендров: {counterRef.current}<br />
-        <input text="text" onChange={handlerChange} value={text} />
-        <button onClick={handlerFocus}>Поставить фокус на поле</button>
-    </div>
-}
-
-function ClickCounter() {
-    const countRef = useRef(0);
-    
-    function handlerClick() {
-        countRef.current += 1;
-        //alert(`Нажали ${countRef.current} раз.`);
-    }
-    return <button onClick={handlerClick}>Нажать</button>;
-}
-
-function TimerComponent() {
-    const timerIdRef = useRef(null);
-    
-    useEffect(() => {
-        timerIdRef.current = setTimeout(() => {
-            alert("Прошло 3 секунды");
-        }, 3000);
-        return () => {
-            clearTimeout(timerIdRef.current);
-        }
+    const handleDelete = useCallback(id => {
+        items.pop(id);
     },[]);
-}
-
-function PrevValue({ value }) {
-    const prevValueRef = useRef();
-    
-    useEffect(() => {
-        prevValueRef.current = value;
-    });
-    return (
-        <div>
-            Текущее значение: {value} <br />
-            Предыдущее значение: {prevValueRef.current}
-        </div>
-    )
-}
-
-function ScrollList() {
-    const listRef = useRef(null);
-    
-    const scrollToBottom = () => {
-        if(listRef.current) {
-            listRef.current.scrollTop = listRef.current.scrollHeight;
-        }
-    }
-        
     return (
         <>
-            <div ref={listRef} 
-               style={{height: 200, overflowY: 'auto', border: '1px solid black'}}>
-                {[...Array(20)].map((_,i)=>(
-                    <div key={i}>Элемент № {i + 1}</div>
+            <h3>List items</h3>
+            {items.map(item => (
+             <TodoItem key={item.id} item={item}
+              onToggle={handleToggle} onDelete={handleDelete} />
              ))}
-            </div>
-            <button onClick={scrollToBottom}>Прокрутить вниз</button>
         </>
     )
 }
 
 function App() {
-    
-    
 	return (
 		<>
+			{/* Добавьте тестовый контент для проверки */}
 			<h1>Hello, React!</h1>
-            <ScrollList />
+            <ItemList items={[
+                {id:1,name:'Первый',done:false},
+                {id:2,name:'Второй',done:false}
+            ]} />
 		</>
 	)
 }