useMemo

package-lock.json

@@ -9,9 +9,7 @@
       "version": "0.0.0",
       "dependencies": {
         "react": "^19.1.0",
-        "react-dom": "^19.1.0",
-        "react-error-boundary": "^6.1.2",
-        "react-router-dom": "^7.17.0"
+        "react-dom": "^19.1.0"
       },
       "devDependencies": {
         "@eslint/js": "^9.25.0",
@@ -1602,19 +1600,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/cookie": {
-      "version": "1.1.1",
-      "resolved": "https://registry.npmjs.org/cookie/-/cookie-1.1.1.tgz",
-      "integrity": "sha512-ei8Aos7ja0weRpFzJnEA9UHJ/7XQmqglbRwnf2ATjcB9Wq874VKH9kfjjirM6UhU2/E5fFYadylyhFldcqSidQ==",
-      "license": "MIT",
-      "engines": {
-        "node": ">=18"
-      },
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/express"
-      }
-    },
     "node_modules/cross-spawn": {
       "version": "7.0.6",
       "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.6.tgz",
@@ -2476,15 +2461,6 @@
         "react": "^19.1.0"
       }
     },
-    "node_modules/react-error-boundary": {
-      "version": "6.1.2",
-      "resolved": "https://registry.npmjs.org/react-error-boundary/-/react-error-boundary-6.1.2.tgz",
-      "integrity": "sha512-3DpCr5HVdZ0caUjYE/kIHBEJN0mNP3ZCgf16c48uJ5TbWjorKVp+YG8W3XqlJ7vJAVNw6wNIImyPXmFydwmyng==",
-      "license": "MIT",
-      "peerDependencies": {
-        "react": "^18.0.0 || ^19.0.0"
-      }
-    },
     "node_modules/react-refresh": {
       "version": "0.17.0",
       "resolved": "https://registry.npmjs.org/react-refresh/-/react-refresh-0.17.0.tgz",
@@ -2495,44 +2471,6 @@
         "node": ">=0.10.0"
       }
     },
-    "node_modules/react-router": {
-      "version": "7.17.0",
-      "resolved": "https://registry.npmjs.org/react-router/-/react-router-7.17.0.tgz",
-      "integrity": "sha512-FDELK7rTMlCHO5+reyXsPlmfr7N1F91lPHsWYfMEGQm/KQ+F4JFM8jGoeQDmDvdTs93Fw9aSilH+uKRb4/jXvQ==",
-      "license": "MIT",
-      "dependencies": {
-        "cookie": "^1.0.1",
-        "set-cookie-parser": "^2.6.0"
-      },
-      "engines": {
-        "node": ">=20.0.0"
-      },
-      "peerDependencies": {
-        "react": ">=18",
-        "react-dom": ">=18"
-      },
-      "peerDependenciesMeta": {
-        "react-dom": {
-          "optional": true
-        }
-      }
-    },
-    "node_modules/react-router-dom": {
-      "version": "7.17.0",
-      "resolved": "https://registry.npmjs.org/react-router-dom/-/react-router-dom-7.17.0.tgz",
-      "integrity": "sha512-fyU2yjGups/hE6Xz0I5ZYbVL8Gx29eCjgpHaRaTaVU+OOAdfRX05KsvyRm0GO8YQwOkhpU3MurW1jyMUJn+zSw==",
-      "license": "MIT",
-      "dependencies": {
-        "react-router": "7.17.0"
-      },
-      "engines": {
-        "node": ">=20.0.0"
-      },
-      "peerDependencies": {
-        "react": ">=18",
-        "react-dom": ">=18"
-      }
-    },
     "node_modules/resolve-from": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/resolve-from/-/resolve-from-4.0.0.tgz",
@@ -2606,12 +2544,6 @@
         "semver": "bin/semver.js"
       }
     },
-    "node_modules/set-cookie-parser": {
-      "version": "2.7.2",
-      "resolved": "https://registry.npmjs.org/set-cookie-parser/-/set-cookie-parser-2.7.2.tgz",
-      "integrity": "sha512-oeM1lpU/UvhTxw+g3cIfxXHyJRc/uidd3yK1P242gzHds0udQBYzs3y8j4gCCW+ZJ7ad0yctld8RYO+bdurlvw==",
-      "license": "MIT"
-    },
     "node_modules/shebang-command": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/shebang-command/-/shebang-command-2.0.0.tgz",

package.json

@@ -4,16 +4,14 @@
   "version": "0.0.0",
   "type": "module",
   "scripts": {
-    "dev": "vite",
+    "dev": "vite", 
     "build": "vite build",
     "lint": "eslint .",
     "preview": "vite preview"
   },
   "dependencies": {
     "react": "^19.1.0",
-    "react-dom": "^19.1.0",
-    "react-error-boundary": "^6.1.2",
-    "react-router-dom": "^7.17.0"
+    "react-dom": "^19.1.0"
   },
   "devDependencies": {
     "@eslint/js": "^9.25.0",

src/App.jsx

@@ -1,25 +1,82 @@
-import { Suspense, lazy } from 'react'
-import { ErrorBoundary } from 'react-error-boundary'
+import memo, { useMemo, useCallback, useState } from 'react'
 
-const LazyComponent = lazy(() => import('./MyComponent'))
-
-function ErrorFallBack({error, resetErrorBoundary }) {
+function MyComponent() {
+    const [count, setCount] = useState(0);
+    const [name, setName] = useState('John');
+    
+    const greeting = useMemo(() => `Hello, ${name}!`,[name]);
+    
     return (
-        <div>
-            <h2>Что то сломалось</h2>
-            <button onClick={resetErrorBoundary}></button>
-        </div>
+        <>
+        <h2>{greeting}</h2>
+        <button onClick={()=>setName('Alex')}>New name</button>
+        </>
+    )
+}
+
+function MyComponent2() {
+    const [data,setData] = useState([{theme:'light'}])
+    const userPreferences = useMemo(()=>({theme: 'dark', language: 'en'}),[]);
+    
+    const processData = useMemo(()=>{
+        return data.map(item => ({ ...item,theme: userPreferences.theme }))
+    },[data, userPreferences]);
+    console.log(processData);
+    return (
+        <>
+            <h2 className={data.theme}>2</h2>
+            <button onClick={()=>setData(data)}>set new theme</button>
+        </>
+    )
+}
+
+function MyComponent3() {
+    const sum = useMemo(()=> a+b,[a,b]);//Бессмысленное применение и вредное
+
+    //Применение оправдано
+    const complexResult = useMemo(()=>{
+        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 (
 		<>
-			<ErrorBoundary FallBackComponent={ErrorFallBack}>
-                <Suspense fallback={<div>Загрузка ...</div>}>
-			        <LazyComponent />
-                </Suspense>
-            </ErrorBoundary>
+			{/* Добавьте тестовый контент для проверки */}
+			<h1>Hello, React!</h1>
+            <ParentComponent items={[{name:'Alex'},{name:'Bob'}]} />
 		</>
 	)
 }

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>
 )