101 lines
2.4 KiB
React
101 lines
2.4 KiB
React
import { useState, useRef, useEffect } from 'react'
|
|
|
|
function Example() {
|
|
const myRef = useRef(null);
|
|
const counterRef = useRef(0);
|
|
const [text, setText] = useState('');
|
|
|
|
useEffect(() => {
|
|
myRef.current?.focus();
|
|
},[]);
|
|
|
|
const handlerFocus = () => {
|
|
if(myRef.current) {
|
|
myRef.current.focus();
|
|
}
|
|
};
|
|
|
|
const handlerChange = (event) => {
|
|
setText(event.target.value);
|
|
}
|
|
counterRef.current += 1;
|
|
return <div>
|
|
<input ref={myRef} text="text" /><br />
|
|
Количество рендров: {counterRef.current}<br />
|
|
<input text="text" onChange={handlerChange} value={text} />
|
|
<button onClick={handlerFocus}>Поставить фокус на поле</button>
|
|
</div>
|
|
}
|
|
|
|
function ClickCounter() {
|
|
const countRef = useRef(0);
|
|
|
|
function handlerClick() {
|
|
countRef.current += 1;
|
|
//alert(`Нажали ${countRef.current} раз.`);
|
|
}
|
|
return <button onClick={handlerClick}>Нажать</button>;
|
|
}
|
|
|
|
function TimerComponent() {
|
|
const timerIdRef = useRef(null);
|
|
|
|
useEffect(() => {
|
|
timerIdRef.current = setTimeout(() => {
|
|
alert("Прошло 3 секунды");
|
|
}, 3000);
|
|
return () => {
|
|
clearTimeout(timerIdRef.current);
|
|
}
|
|
},[]);
|
|
}
|
|
|
|
function PrevValue({ value }) {
|
|
const prevValueRef = useRef();
|
|
|
|
useEffect(() => {
|
|
prevValueRef.current = value;
|
|
});
|
|
return (
|
|
<div>
|
|
Текущее значение: {value} <br />
|
|
Предыдущее значение: {prevValueRef.current}
|
|
</div>
|
|
)
|
|
}
|
|
|
|
function ScrollList() {
|
|
const listRef = useRef(null);
|
|
|
|
const scrollToBottom = () => {
|
|
if(listRef.current) {
|
|
listRef.current.scrollTop = listRef.current.scrollHeight;
|
|
}
|
|
}
|
|
|
|
return (
|
|
<>
|
|
<div ref={listRef}
|
|
style={{height: 200, overflowY: 'auto', border: '1px solid black'}}>
|
|
{[...Array(20)].map((_,i)=>(
|
|
<div key={i}>Элемент № {i + 1}</div>
|
|
))}
|
|
</div>
|
|
<button onClick={scrollToBottom}>Прокрутить вниз</button>
|
|
</>
|
|
)
|
|
}
|
|
|
|
function App() {
|
|
|
|
|
|
return (
|
|
<>
|
|
<h1>Hello, React!</h1>
|
|
<ScrollList />
|
|
</>
|
|
)
|
|
}
|
|
|
|
export default App
|