useMemo

package-lock.json

@@ -8,7 +8,6 @@
       "name": "store-client",
       "version": "0.0.0",
       "dependencies": {
-        "@tanstack/react-query": "^5.100.14",
         "react": "^19.1.0",
         "react-dom": "^19.1.0"
       },
@@ -1305,32 +1304,6 @@
         "win32"
       ]
     },
-    "node_modules/@tanstack/query-core": {
-      "version": "5.100.14",
-      "resolved": "https://registry.npmjs.org/@tanstack/query-core/-/query-core-5.100.14.tgz",
-      "integrity": "sha512-5X41dGpxgeaHISCRW2oYwcSycZeULZzAunaudXT9ov1KOTj9xwt0CH6hbwqP1/z74ZWF7rYFnDpyYH07XFcZew==",
-      "license": "MIT",
-      "funding": {
-        "type": "github",
-        "url": "https://github.com/sponsors/tannerlinsley"
-      }
-    },
-    "node_modules/@tanstack/react-query": {
-      "version": "5.100.14",
-      "resolved": "https://registry.npmjs.org/@tanstack/react-query/-/react-query-5.100.14.tgz",
-      "integrity": "sha512-oOr6aRdSFEwWhzxEkD/9ZcItM3+LjBSkeVmadWKwUssAHTsqd/7bOjWrX4AbvEkoEhgAxzN0Xk6H/aYzXiYBAw==",
-      "license": "MIT",
-      "dependencies": {
-        "@tanstack/query-core": "5.100.14"
-      },
-      "funding": {
-        "type": "github",
-        "url": "https://github.com/sponsors/tannerlinsley"
-      },
-      "peerDependencies": {
-        "react": "^18 || ^19"
-      }
-    },
     "node_modules/@types/babel__core": {
       "version": "7.20.5",
       "resolved": "https://registry.npmjs.org/@types/babel__core/-/babel__core-7.20.5.tgz",

package.json

@@ -4,13 +4,12 @@
   "version": "0.0.0",
   "type": "module",
   "scripts": {
-    "dev": "vite",
+    "dev": "vite", 
     "build": "vite build",
     "lint": "eslint .",
     "preview": "vite preview"
   },
   "dependencies": {
-    "@tanstack/react-query": "^5.100.14",
     "react": "^19.1.0",
     "react-dom": "^19.1.0"
   },

src/App.jsx

@@ -1,93 +1,82 @@
-import React, {useState, useEffect, useRef } from 'react'
-//import { useQuery } from '@tanstack/react-query'
+import memo, { useMemo, useCallback, useState } from 'react'
 
-function useWindowWidth() {
-    const [width,setWidth] = useState(window.innerWidth)
+function MyComponent() {
+    const [count, setCount] = useState(0);
+    const [name, setName] = useState('John');
     
-    useEffect(() => {
-        const handleResize = () => setWidth(window.innerWidth);
-        window.addEventListener('resize',handleResize);
-        return () => window.removeEventListener('resize',handleResize);
-    },[])
+    const greeting = useMemo(() => `Hello, ${name}!`,[name]);
     
-    return width
-}
-
-function useLocalStorage(key, initValue) {
-    const [value, setValue] = useState(()=>{
-        const stored = localStorage.getItem(key);
-        return stored !== null ? JSON.parse(stored) : initValue
-    })
-    
-    useEffect(() => {
-        localStorage.setItem(key, JSON.stringify(value))
-    },[key, value])
-    
-    return [value,setValue]
-}
-/*
-function useUserData(userId) {
-    return useQuery(
-        ['user',userId],
-        () => fetch(`/api/user/${userId}`).then(res => res.json()),
-        {refetchOnWindowFocus: false}
+    return (
+        <>
+        <h2>{greeting}</h2>
+        <button onClick={()=>setName('Alex')}>New name</button>
+        </>
     )
-}*/
-
-function useInput(initValue, validate) {
-    const [value, setValue] = useState(initValue);
-    const [error, setError] = useState(null);
-    
-    const onChange = e => {
-        const newValue = e.target.value
-        setValue(newValue)
-        if (validate) {
-            const validationResult = validate(newValue)
-            setError(validationResult)
-        }
-    }
-    
-    return { value, error, onChange }
 }
 
-function useInterval(callback, delay) {
-    const savedCallback = useRef()
+function MyComponent2() {
+    const [data,setData] = useState([{theme:'light'}])
+    const userPreferences = useMemo(()=>({theme: 'dark', language: 'en'}),[]);
     
-    useEffect(()=>{
-        savedCallback.current = callback
-    },[callback]);
+    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('');
     
-    useEffect(()=>{
-        if (delay == null) return
-        const id = setInterval(()=>{
-            savedCallback.current()
-        },delay);
-        return () => clearInterval(id);
-    },[delay])
+    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() {
-    const width = useWindowWidth();
-    const [theme, setTheme] = useLocalStorage('theme','light');
-    
-    const username = useInput(
-        '',
-        value => value.length < 3 ? 'минимум 3 символа' : null
-    )
-    
 	return (
 		<>
-			<h1>Hello, React!{width}</h1>
-            <button onClick={()=>{
-                setTheme(theme === 'light' ? 'dark' : 'light')
-            }}>
-                Сменить тему
-            </button>
-            <p><input type="text" 
-                value={username.value} 
-                onChange={username.onChange} />
-                { username.error ? username.error : '' }
-            </p>
+			{/* 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>
 )