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JavaScript React Components (2018) Stateful Components and Lifecycle Methods Resetting the Stopwatch

Alena Miadzvedskaya
Alena Miadzvedskaya
6,386 Points
Posted by Alena Miadzvedskaya
Alena Miadzvedskaya
6,386 Points

Can't stop the timer, it still ticks even after stop button was clicked

const Stopwatch = () => { const [isRunning, setIsRunning] = useState(false); const [elapsedTime, setElapsedTime] = useState(0); const [prevTime, setPrevTime] = useState(0);

const intervalID = () => { setInterval(() => tick(), 1000)}

const stopTimer = () => { clearInterval(intervalID) }

const handleStopwatch = () => { setIsRunning(!isRunning); if (!isRunning) { setPrevTime(Date.now()); } };

useEffect(() => { if(isRunning) { intervalID() } else { stopTimer() } }, [isRunning]);

const tick = () => { if (isRunning === true) { const now = Date.now(); const elapsedTimeNow = elapsedTime; const prevTimeNow = prevTime; setPrevTime(now); setElapsedTime(elapsedTimeNow + (now - prevTimeNow)); } };

const seconds = Math.floor(elapsedTime / 1000)

return ( <div className="stopwatch"> <h2>Stopwatch</h2> <span className="stopwatch-time">{ seconds }</span> <button onClick={handleStopwatch}>{isRunning ? "Stop" : "Start"}</button> <button>Reset</button> </div> ); };