React js简单钩子效果

import React, { useState } from 'react';

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

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

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

function DataFetcher() {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => setData(data));
  }, []);

  return (
    <div>
      {data ? <p>Data: {data}</p> : <p>Loading...</p>}
    </div>
  );
}

import React, { useContext } from 'react';

const ThemeContext = React.createContext('light');

function ThemeButton() {
  const theme = useContext(ThemeContext);

  return (
    <button style={{ background: theme }}>Button</button>
  );
}