useMemo

package-lock.json

@@ -8,7 +8,6 @@
       "name": "store-client",
       "version": "0.0.0",
       "dependencies": {
-        "immer": "^11.1.8",
         "react": "^19.1.0",
         "react-dom": "^19.1.0"
       },
@@ -2055,16 +2054,6 @@
         "node": ">= 4"
       }
     },
-    "node_modules/immer": {
-      "version": "11.1.8",
-      "resolved": "https://registry.npmjs.org/immer/-/immer-11.1.8.tgz",
-      "integrity": "sha512-/tbkHMW7y10Lx6i1crLjD4/OhNkRG+Fo7byZHtah0547nIeXYcpIXaUh0IAQY6gO5459qpGGYapcEOHtFXkIuA==",
-      "license": "MIT",
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/immer"
-      }
-    },
     "node_modules/import-fresh": {
       "version": "3.3.1",
       "resolved": "https://registry.npmjs.org/import-fresh/-/import-fresh-3.3.1.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": {
-    "immer": "^11.1.8",
     "react": "^19.1.0",
     "react-dom": "^19.1.0"
   },

src/App.jsx

@@ -1,49 +1,82 @@
-import React, { useState, useEffect } from 'react'
-import { produce } from 'immer'
+import memo, { useMemo, useCallback, useState } from 'react'
+
+function MyComponent() {
+    const [count, setCount] = useState(0);
+    const [name, setName] = useState('John');
+    
+    const greeting = useMemo(() => `Hello, ${name}!`,[name]);
+    
+    return (
+        <>
+        <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() {
-    const [tasks,setTasks] = useState([])
-    const [input,setInput] = useState('')
-    
-    const addTask = () => {
-        if(!input.trim()) return
-        
-        setTasks(currentTasks => produce(currentTasks, draft => {
-            draft.push({
-                id: Date.now(),
-                text: input.trim(),
-                done: false
-            })
-        }))
-        setInput('')
-    }
-    const toggleTask = id => {
-        setTasks(currentTask => produce(currentTask, draft => {
-            const task = draft.find(t => t.id === id)
-            if(task) {
-                task.done = !task.done
-            }
-        }))
-    }
-    const removeTask = id => {
-        setTasks(currentTask => produce(currentTask, draft => {
-            const index = draft.findIndex(t => t.id === id)
-            if (index !== -1)
-                draft.splice(index,1)
-        }))
-    }
 	return (
 		<>
-			<h1>Практика по созданию списка задач</h1>
-            <input value={input} onChange={e=>setInput(e.target.value)} />
-            <button onClick={addTask}>Добавить</button>
-        <ul>{tasks.map(({id,text,done}) => (
-                <li key={id} style={{ textDecoration: done ? 'line-through' : 'none'}}>
-                <input type="checkbox" checked={done} onChange={()=> toggleTask(id)} />
-                {text}
-                <button onClick={() => removeTask(id)}>Удалить</button>
-                </li>
-            ))}</ul>
+			{/* Добавьте тестовый контент для проверки */}
+			<h1>Hello, React!</h1>
+            <ParentComponent items={[{name:'Alex'},{name:'Bob'}]} />
 		</>
 	)
 }

src/MyComponent.jsx

@@ -1,8 +0,0 @@
-export function MyComponent() {
-    return (
-        <>
-        <h1>Hello</h1>
-        </>
-    )
-}
-export default MyComponent