react js 定时器

import React, { useEffect } from 'react';

function DelayedComponent() {
  useEffect(() => {
    const timer = setTimeout(() => {
      console.log('This runs after 3 seconds');
    }, 3000);

    // Cleanup function to clear the timer when the component is unmounted
    return () => clearTimeout(timer);
  }, []);

  return <div>Check the console after 3 seconds</div>;
}

export default DelayedComponent;

import React, { useState, useEffect } from 'react';

function Counter() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    const intervalId = setInterval(() => {
      setCount(prevCount => prevCount + 1);
    }, 1000);

    // Cleanup function to clear the interval when the component is unmounted
    return () => clearInterval(intervalId);
  }, []);

  return <div>Count: {count}</div>;
}

export default Counter;

useEffect(() => {
  const timer = setTimeout(() => {
    // Your code here
  }, 1000);

  return () => clearTimeout(timer); // Cleanup function
}, []);

useEffect(() => {
  let isMounted = true;

  const timer = setTimeout(() => {
    if (isMounted) {
      setCount(prevCount => prevCount + 1);
    }
  }, 1000);

  return () => {
    isMounted = false;
    clearTimeout(timer);
  };
}, []);