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Avoiding Unnecessary Firing

We may choose to use the functional update form to avoid firing an effect.
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<!DOCTYPE html><html>
  <head>
    <meta charset="UTF-8" />
    <script src="https://unpkg.com/react@18/umd/react.development.js" crossorigin></script>
    <script src="https://unpkg.com/react-dom@18/umd/react-dom.development.js" crossorigin></script>
    <script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
  </head>
  <body>
    <div></div>
    <script type="text/babel">
      function Counter() {
        const [count, setCount] = React.useState(0);
        React.useEffect(() => {
          console.log(999);  // not executed repeatedly
          const id = setInterval(() => {     // setCount(count+1);  // count always 0 here. works if [count] is the dependency.
            setCount(c => c + 1); // this doesn't depend on the `count` variable outside
          }, 1000);
          return () => clearInterval(id);
        }, []); // this effect doesn't use any variables in the component scope
        return <h1>{count}</h1>;
      }
      const root = ReactDOM.createRoot(document.querySelector("div"));
      root.render(<Counter/>);
    </script>
  </body></html>