reactjs-interview-coding/stopwatch.js at master · enterthevoid8/reactjs-interview-coding · GitHub

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import { useEffect, useState } from "react";

export default function Stopwatch() {
  const [seconds, setSeconds] = useState(0);
  const [running, setRunning] = useState(false);

  useEffect(() => {
    if (!running) return;

    const intervalId = setInterval(() => {
      setSeconds((prev) => prev + 1);
    }, 1000);

    return () => {
      clearInterval(intervalId);
    };
  }, [running]);

  return (
    <div>
      <h2>{seconds}s</h2>

      <button onClick={() => setRunning(true)}>Start</button>
      <button onClick={() => setRunning(false)}>Stop</button>
      <button
        onClick={() => {
          setRunning(false);
          setSeconds(0);
        }}
      >
        Reset
      </button>
    </div>
  );
}