Сделали React.memo и React.useMemo

src/App.jsx

@@ -1,59 +1,60 @@
-import React from 'react'
+import { memo, useState, useMemo } from 'react'
 
-class RandomUser extends React.Component {
-    constructor(props) {
-        super(props)
-        this.state = { user: {} }
-    }
-    
-    componentDidMount() {
-        fetch('https://randomuser.me/api')
-        .then(responce => responce.json())
-        .then(json => this.setState({ user: json.results[0] }));
-        console.log('смонтирован')
-    }
-    
-    componentDidUpdate(prevProps,prevState) {
-        console.log(this.state);
-        console.log('Компонент обнвлен')
-    }
-    
-    componentWillUnmount() {
-        console.log('Компонент таймера размонтирован')
-    }
-    
-    render() {
-        return <div>
-            {this.state.user && 
-                this.state.user.name &&
-                (
-                <>
-                    <h2>{this.state.user.name.first} {this.state.user.name.last}</h2>
-                    <img src={this.state.user.picture.medium} />
-                    <button onClick={() => {
-                        console.log('Загружаем ... ')
-                        fetch('https://randomuser.me/api')
-                        .then(responce => responce.json())
-                        .then(json => this.setState({ user: json.results[0] }));
-                    }}>Загрузить нового</button>
-                </>
-                )
-            }
-            </div>
+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 App() {
-    const [showClock, setShowClock] = React.useState(true);
+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 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 (
+        <>
+            <Child>
+                {stableChild}
+            </Child>
+            <input type="text" onChange={(e) => setText(e.target.value)} value={text} />
+            <button onClick={() => setCount(count + 1)}>Increment {count}</button>
+        </>
+    )
+}
+
+function App() {
 	return (
 		<>
-			<h1>Домашнее задание: жизненый цикл</h1>
-            <button onClick={()=> setShowClock(!showClock)}>
-                {showClock ? 'Скрыть часы' : 'Показать часы' }
-            </button>
-            {showClock && <RandomUser />}
-		</>
+			<h1>Hello, React!</h1>
+            <Parent />
+        </>
 	)
 }