useMemo

2026-05-26 20:59:44 +03:00
8 changed files with 72 additions and 216 deletions
@@ -5,19 +5,6 @@
 		<link rel="icon" type="image/svg+xml" href="/vite.svg" />
 		<meta name="viewport" content="width=device-width, initial-scale=1.0" />
 		<title>Vite + React</title>
 		<style>
 			* {
 				margin: 0;
 				padding: 0;
 				box-sizing: border-box;
 				font-family: Arial, Helvetica, sans-serif;
 			}
 			body {
 				background-color: #ecfeff;
 			}
 		</style>
 	</head>
 	<body>
 		<div id="root"></div>
@@ -20,7 +20,6 @@
        "eslint-plugin-react-hooks": "^5.2.0",
        "eslint-plugin-react-refresh": "^0.4.19",
        "globals": "^16.0.0",
        "react-icons": "^5.6.0",
        "vite": "^6.3.5"
      }
    },
@@ -2462,16 +2461,6 @@
        "react": "^19.1.0"
      }
    },
    "node_modules/react-icons": {
      "version": "5.6.0",
      "resolved": "https://registry.npmjs.org/react-icons/-/react-icons-5.6.0.tgz",
      "integrity": "sha512-RH93p5ki6LfOiIt0UtDyNg/cee+HLVR6cHHtW3wALfo+eOHTp8RnU2kRkI6E+H19zMIs03DyxUG/GfZMOGvmiA==",
      "dev": true,
      "license": "MIT",
      "peerDependencies": {
        "react": "*"
      }
    },
    "node_modules/react-refresh": {
      "version": "0.17.0",
      "resolved": "https://registry.npmjs.org/react-refresh/-/react-refresh-0.17.0.tgz",
@@ -4,7 +4,7 @@
  "version": "0.0.0",
  "type": "module",
  "scripts": {
-    "dev": "vite",
+    "dev": "vite", 
    "build": "vite build",
    "lint": "eslint .",
    "preview": "vite preview"
@@ -22,7 +22,6 @@
    "eslint-plugin-react-hooks": "^5.2.0",
    "eslint-plugin-react-refresh": "^0.4.19",
    "globals": "^16.0.0",
    "react-icons": "^5.6.0",
    "vite": "^6.3.5"
  }
 }
@@ -1,72 +1,82 @@
-import styles from './App.module.css'
+import memo, { useMemo, useCallback, useState } from 'react'
 import SneakersImage from './assets/images/sneakers-image.jpg'
 import { FaRegUser } from 'react-icons/fa'
-function handleClick(i) {
+function MyComponent() {
-    console.log(i);
+    const [count, setCount] = useState(0);
-}
+    const [name, setName] = useState('John');
-
+    
-function Header() {
+    const greeting = useMemo(() => `Hello, ${name}!`,[name]);
-    const handleChange = event => {
+    
        const newValue = event.target.value;
        console.log(`Новое значение ${newValue}`);
    }
    return (
-		<header className={styles.header}>
+        <>
-			<div>
+        <h2>{greeting}</h2>
-				<h2>Store</h2>
+        <button onClick={()=>setName('Alex')}>New name</button>
-				<input type='text	' placeholder='Search...' onChange={handleChange} />
+        </>
-			</div>
+    )
 			<div>
 				<FaRegUser size={24} color='#3258e3' />
 				<button>Profile</button>
 			</div>
 		</header>
 	)
 }
-function Product() {
+function MyComponent2() {
-    const handlerMouseEnter = event => {
+    const [data,setData] = useState([{theme:'light'}])
-        const img = event.target;
+    const userPreferences = useMemo(()=>({theme: 'dark', language: 'en'}),[]);
-        img.style.border = '5px solid yellow';
+    
-    }
+    const processData = useMemo(()=>{
-    const handlerMouseOut = event => {
+        return data.map(item => ({ ...item,theme: userPreferences.theme }))
-        const img = event.target;
+    },[data, userPreferences]);
-        img.style.border = '';
+    console.log(processData);
-        console.log(event);
+    return (
-    }
+        <>
-	return (
+            <h2 className={data.theme}>2</h2>
-		<div className={styles.product}>
+            <button onClick={()=>setData(data)}>set new theme</button>
-			<img src={SneakersImage} alt='' onMouseEnter={handlerMouseEnter} onMouseOut={handlerMouseOut} />
+        </>
-			<div className={styles.content}>
+    )
-				<div className={styles.title}>
+}
-					<h4>Sneakers Red & White 2025</h4>
+
-					<button onClick={() => handleClick(0)} onMouseEnter={handlerMouseEnter} onMouseOut={handlerMouseOut}>+</button>
+function MyComponent3() {
-				</div>
+    const sum = useMemo(()=> a+b,[a,b]);//Бессмысленное применение и вредное
-				<p className={styles.description}>NIKE</p>
+
-				<p className={styles.price}>$38.00</p>
+    //Применение оправдано
-			</div>
+    const complexResult = useMemo(()=>{
-		</div>
+        return heavyMethOperations(largeDataSet);
-	)
+    },[largeDataSet])
 }
 function ParentComponent({ items }) {
    const [filter, setFilter] = useState('');
    const listProps = useMemo(()=>({
            items: items.filter(item => item.name.includes(filter)),
            onItemClick: id => console.log('Clicked',id),
            theme: 'dark'
        }),[items,filter]);
    return (
        <>
        <Memoized {...listProps} />
        <button onClick={()=>setFilter('Bob')}>Click</button>
        </>
    )
 }
 function Memoized(props) {
    console.log(props);
    return (
        <>
        <h3 className={props.theme}>Memoized</h3>
        {props.items.map((item) => (
         <>
            <li>
                {item.name}
            </li>
         </>))}
        </>
    )
 }
 function App() {
 	return (
 		<>
-			<div className={styles.container}>
+			{/* Добавьте тестовый контент для проверки */}
-			<Header />
+			<h1>Hello, React!</h1>
-				<ul className={styles.list}>
+            <ParentComponent items={[{name:'Alex'},{name:'Bob'}]} />
 					<li>
 						<Product />
 					</li>
 					<li>
 						<Product />
 					</li>
 					<li>
 						<Product />
 					</li>
 				</ul>
 			</div>
 		</>
 	)
 }
@@ -1,123 +0,0 @@
@use './assets/styles/variables' as *;
 .header {
 	display: flex;
 	justify-content: space-between;
 	align-items: center;
 	padding: 20px;
 	background-color: white;
 	border-bottom-left-radius: 10px;
 	border-bottom-right-radius: 10px;
 	div {
 		&:first-child {
 			display: flex;
 			align-items: center;
 			gap: 20px;
 			h2 {
 				color: $primary-color;
 			}
 			input {
 				border-radius: 5px;
 				outline: none;
 				font-size: 16px;
 				border: 1px solid gainsboro;
 				padding: 5px 10px;
 				&:focus {
 					border: 1px solid $primary-color;
 				}
 			}
 		}
 		&:last-child {
 			display: flex;
 			align-items: center;
 			gap: 10px;
 			button {
 				outline: 0;
 				border: 0;
 				border-radius: 5px;
 				padding: 5px 15px;
 				font-size: 16px;
 				background-color: $primary-color;
 				color: $white-color;
 				font-weight: 600;
 				cursor: pointer;
 				&:hover {
 					background-color: $seconday-color;
 				}
 			}
 		}
 	}
 }
 .container {
 	max-width: 1220px;
 	margin: 0 auto;
 }
 .list {
 	display: flex;
 	justify-content: space-between;
 	border-radius: 10px;
 	margin-top: 100px; /* временно */
 	padding: 20px;
 	background-color: white;
 	list-style: none;
 }
 .product {
 	display: flex;
 	flex-direction: column;
 	width: 350px;
 	gap: 20px;
 	border-radius: 10px;
 }
 .content {
 	display: flex;
 	flex-direction: column;
 	gap: 10px;
 }
 .title {
 	display: flex;
 	justify-content: space-between;
 	align-items: center;
 	h4 {
 		font-size: 18px;
 	}
 	button {
 		background-color: black;
 		color: white;
 		border: 0;
 		border-radius: 50%;
 		outline: 0;
 		font-size: 20px;
 		padding: 5px 10px;
 		cursor: pointer;
 	}
 }
 img {
 	border-radius: 10px;
 }
 .description {
 	color: gray;
 }
 .price {
 	font-weight: bold;
 }
@@ -1,5 +0,0 @@
 $white-color: white;
 $black-color: black;
 $primary-color: #3258e3;
 $seconday-color: #4432e3;
@@ -1,9 +1,8 @@
 import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 // удаляем import './index.css'
 import App from './App.jsx'
 createRoot(document.getElementById('root')).render(
 	<StrictMode>
 		<App />
 	</StrictMode>
 )