StopWatch.js

import React, { useState } from "react"
let intervalId;

function StopWatch() {
  const [counter, setCounter] = useState(0)
  const handleClick = (action) => {
    switch(action){
      case 'start' : {
        intervalId = setInterval(() => {
          setCounter((prev) => prev + 1)
        },1000)
        break;
      }
      case 'pause' : {
        clearInterval(intervalId);
        intervalId = null;
        break;
      }
      case 'reset' : {
        clearInterval(intervalId); 
        intervalId = null       
        setCounter(0)
        break;
      }
      default : {

      }
    }
  }
  return (
    <div>
      <h1>{counter}</h1>
      <button onClick={() => handleClick('start')}>Start</button>
      <button onClick={() => handleClick('pause')}>Pause</button>
      <button onClick={() => handleClick('reset')}>Reset</button>
    </div>
  )
}
export default StopWatch