Сделали React.memo и React.useMemo

src/App.jsx

@@ -1,67 +1,60 @@
-import React, { useState, useReducer, useRef, memo } from 'react'
+import { memo, useState, useMemo } from 'react'
 
-function tasksReducer(state, action) {
+function memoize(fn) {
-    switch(action.type) {
+    const cache = new Map();
-        case 'ADD_TASK':
+    return function(...args) {
-            return [...state, action.payload]
+        const key = JSON.stringify(args);
-        case 'TOGGLE_TASK':
+        if (cache.has(key)) {
-            return state.map(task => task.id === action.payload ? {...task, complite: !task.complite} : task)
+            return cache.get(key);
-        case 'REMOVE_TASK':
+        }
-            return state.filter(task => task.id !== action.payload)
+        const result = fn.apply(this, args);
-        default:
+        cache.set(key,result);
-            return state
+        return result;
     }
 }
 
-const TaskList = memo(function TaskList({tasks, onToggle, onRemove}) {
+function fibonachi(n, memo={}) {
-    console.log("Rendred")
+    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 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>,[]);
+    
     return (
-        <ul>
+        <>
-        {tasks.map(({id, text, complite}) => (
+            <Child>
-                <li key={id}
+                {stableChild}
-                    style={{textDecoration: complite ? 'line-through' : 'none' }}>
+            </Child>
-                    <input type="checkbox" checked={complite} onChange={()=>onToggle(id)} />
+            <input type="text" onChange={(e) => setText(e.target.value)} value={text} />
-                    {text}
+            <button onClick={() => setCount(count + 1)}>Increment {count}</button>
-                    <button onClick={()=> onRemove(id)} style={{marginLeft: 10}}>
+        </>
-                        Удалить
-                    </button>
-                </li>
-            ))}
-        </ul>
     )
-})
+}
 
 function App() {
-    const [tasks, dispatch] = useReducer(tasksReducer,[])
-    const [input,setInput] = useState('')
-    const [error,setError] = useState('')
-    const inputRef = useRef(null)
-    
-    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 style={{padding: 20}}>
+		<>
-			<h1>Список дел</h1>
+			<h1>Hello, React!</h1>
-			<input ref={inputRef} value={input} onChange={e => setInput(e.target.value)} />
+            <Parent />
-			<button onClick={addTask}>Добавить</button>
+        </>
-            {error && <p style={{color: 'red'}}>{error}</p>}
-            
-            <TaskList tasks={tasks} 
-                onToggle={id => dispatch({type: 'TOGGLE_TASK', payload: id})}
-                onRemove={id => dispatch({type: 'REMOVE_TASK', payload: id})} />
-		</div>
 	)
 }
 

src/main.jsx

@@ -4,7 +4,5 @@ import { createRoot } from 'react-dom/client'
 import App from './App.jsx'
 
 createRoot(document.getElementById('root')).render(
-	<StrictMode>
 		<App />
-	</StrictMode>
 )