Watch: Adding a Lap Logger to a React Stopwatch

This tutorial extends our React stopwatch to include lap timing functionality – a crucial feature for any serious timekeeping application. We'll leverage our knowledge of React state management, arrays, and conditional rendering to achieve this. This is part 3 of the Building a Stopwatch in React series.

Frequently Asked Questions (FAQs) about Adding Lap Logging to a React Stopwatch

How to Add Lap Logging to a React Stopwatch?

Adding lap logging requires a function triggered by a "Lap" button. This function captures the stopwatch's current time and adds it to an array. The useState hook manages this array.

const [laps, setLaps] = useState([]);

const handleLap = () => {
  setLaps([...laps, currentTime]);
};

Displaying Lap Times

Display lap times by mapping over the laps array, rendering a component for each lap:

{laps.map((lap, index) => (
  <p key={index}>Lap {index + 1}: {lap}</p>
))}

Formatting Lap Times

Improve readability by converting milliseconds to minutes, seconds, and milliseconds using a helper function:

const formatTime = (time) => {
  const minutes = Math.floor(time / 60000);
  const seconds = Math.floor((time - minutes * 60000) / 1000);
  const milliseconds = time - minutes * 60000 - seconds * 1000;
  return `${minutes}:${seconds}:${milliseconds}`;
};

Resetting Lap Times

Resetting lap times involves clearing the laps array:

const handleReset = () => {
  setLaps([]);
  // ...reset stopwatch...
};

Ensuring Accurate Lap Times

Accuracy is paramount. The lap logging function should be synchronous to avoid delays in capturing the current time.

Adding Pause Functionality

Introduce a state variable to track whether the stopwatch is running:

const [isRunning, setIsRunning] = useState(false);

// ...in the time increment function...
if (isRunning) {
  // ...increment time...
}

Resuming from Pause

Preserve the current time when pausing; only reset it during a full reset.

Implementing Lap Functionality (already covered above)

Persisting Lap Times Across Refreshes

Use localStorage to store lap times, ensuring persistence even after page refreshes:

const handleLap = () => {
  const newLaps = [...laps, currentTime];
  setLaps(newLaps);
  localStorage.setItem('laps', JSON.stringify(newLaps));
};

Responsive Design

Use CSS media queries to adjust the layout and sizing for different viewport sizes:

@media (max-width: 600px) {
  .stopwatch {
    font-size: 20px;
  }
  .lap-logger {
    font-size: 16px;
  }
}

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