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@@ -1,82 +1,58 @@
import memo, { useMemo, useCallback, useState } from 'react' import React from 'react'
function MyComponent() { class RandomUser extends React.Component {
const [count, setCount] = useState(0); constructor(props) {
const [name, setName] = useState('John'); super(props)
this.state = { user: {} }
}
const greeting = useMemo(() => `Hello, ${name}!`,[name]); componentDidMount() {
fetch('https://randomuser.me/api')
.then(responce => responce.json())
.then(json => this.setState({ user: json.results[0] }));
console.log('смонтирован')
}
return ( componentDidUpdate(prevProps,prevState) {
<> console.log(this.state);
<h2>{greeting}</h2> console.log('Компонент обнвлен')
<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(()=>{ componentWillUnmount() {
return data.map(item => ({ ...item,theme: userPreferences.theme })) console.log('Компонент таймера размонтирован')
},[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(()=>({ render() {
items: items.filter(item => item.name.includes(filter)), return <div>
onItemClick: id => console.log('Clicked',id), {this.state.user &&
theme: 'dark' this.state.user.name &&
}),[items,filter]); (
<>
return ( <h2>{this.state.user.name.first} {this.state.user.name.last}</h2>
<> <img src={this.state.user.picture.medium} />
<Memoized {...listProps} /> <button onClick={() => {
<button onClick={()=>setFilter('Bob')}>Click</button> console.log('Загружаем ... ')
</> fetch('https://randomuser.me/api')
) .then(responce => responce.json())
} .then(json => this.setState({ user: json.results[0] }));
}}>Загрузить нового</button>
function Memoized(props) { </>
console.log(props); )
return ( }
<> </div>
<h3 className={props.theme}>Memoized</h3> }
{props.items.map((item) => (
<>
<li>
{item.name}
</li>
</>))}
</>
)
} }
function App() { function App() {
const [showClock, setShowClock] = React.useState(true);
return ( return (
<> <>
{/* Добавьте тестовый контент для проверки */} <h1>Домашнее задание: жизненый цикл</h1>
<h1>Hello, React!</h1> <button onClick={()=> setShowClock(!showClock)}>
<ParentComponent items={[{name:'Alex'},{name:'Bob'}]} /> {showClock ? 'Скрыть часы' : 'Показать часы' }
</button>
{showClock && <RandomUser />}
</> </>
) )
} }