Сделали React.memo и React.useMemo

src/App.jsx

@@ -1,32 +1,50 @@
-import React, { useMemo, useCallback, useState } from 'react'
+import { memo, useState, useMemo } from 'react'
 
-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>
-})
+function memoize(fn) {
+    const cache = new Map();
+    return function(...args) {
+        const key = JSON.stringify(args);
+        if (cache.has(key)) {
+            return cache.get(key);
+        }
+        const result = fn.apply(this, args);
+        cache.set(key,result);
+        return result;
+    }
+}
 
-function ItemList({ items }) {
+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];
+}
 
-    const handleToggle = useCallback(id => {
-        items.done = true;
-        console.log(`Item ${id} done`)
-        console.log(id)
-    },[]);
+const MyComponent = ({ value }) => {
+    console.log('Rendring');
+    return <div>{value}</div>
+}
+
+const MemoizedComponent = memo(MyComponent);
+
+const Child = memo(({ children }) => {
+    console.log('Child component rendred');
+    return <div>{children}</div>;
+});
+
+const Parent = () => {
+    const [count,setCount] = useState(0);
+    const [text, setText] = useState('');
+    
+    const stableChild = useMemo(() => <span>Memo text</span>,[]);
     
-    const handleDelete = useCallback(id => {
-        items.pop(id);
-    },[]);
     return (
         <>
-            <h3>List items</h3>
-            {items.map(item => (
-             <TodoItem key={item.id} item={item}
-              onToggle={handleToggle} onDelete={handleDelete} />
-             ))}
+            <Child>
+                {stableChild}
+            </Child>
+            <input type="text" onChange={(e) => setText(e.target.value)} value={text} />
+            <button onClick={() => setCount(count + 1)}>Increment {count}</button>
         </>
     )
 }
@@ -34,13 +52,9 @@ function ItemList({ items }) {
 function App() {
 	return (
 		<>
-			{/* Добавьте тестовый контент для проверки */}
 			<h1>Hello, React!</h1>
-            <ItemList items={[
-                {id:1,name:'Первый',done:false},
-                {id:2,name:'Второй',done:false}
-            ]} />
-		</>
+            <Parent />
+        </>
 	)
 }