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Serg Shevchenko's questions

Martin Hope
Serg Shevchenko
Asked: 2024-11-17 17:34:32 +0800 CST
  • 4

经典示例，并不清楚为什么具有直接值的 setter 不起作用 setCount(count+1) 应用程序仅包含 1 并停止计数，但是每秒都会调用间隔函数，如果我们放置日志，我们就可以看到它。

const { useState, useEffect } = React;

const Counter = () => {
  const [count, setCount] = useState(0);
  useEffect(() => {
    const id = setInterval(() => setCount(count+1), 1000);
    // this set count works
    // const id = setInterval(() => setCount(c => c + 1), 1000);

    return () => clearInterval(id);
  }, []);

return (<div>{count}<button onClick={()=>setCount(10)}>Give10</button></div>);
};

ReactDOM
  .createRoot(root)
  .render(<Counter/ >);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/18.3.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/18.3.1/umd/react-dom.production.min.js"></script>

<div id="root"></div>

reactjs