Javascript Date Range Picker

<div class="container">
  <h1>Date Range Picker</h1>

  <div class="input-group">
    <div class="date-input">
      <label for="startDate">Start Date</label>
      <input type="date" id="startDate">
    </div>

    <div class="date-input">
      <label for="endDate">End Date</label>
      <input type="date" id="endDate">
    </div>
  </div>

  <div id="errorMessage" class="error-message" style="display: none;"></div>

  <div class="result" id="result" style="display: none;">
    <div class="result-item">
      <div class="result-label">Selected Range</div>
      <div class="result-value" id="dateRange">-</div>
    </div>
    <div class="result-item">
      <div class="result-label">Total Days</div>
      <div class="result-value" id="totalDays">-</div>
    </div>
  </div>

  <button class="clear-btn" id="clearBtn">Clear Selection</button>
</div>

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px;
}

.container {
  background: white;
  border-radius: 12px;
  padding: 32px;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
  max-width: 500px;
  width: 100%;
}

h1 {
  font-size: 24px;
  color: #2d3748;
  margin-bottom: 24px;
  text-align: center;
}

.input-group {
  display: flex;
  gap: 12px;
  margin-bottom: 20px;
}

.date-input {
  flex: 1;
  position: relative;
}

.date-input label {
  display: block;
  font-size: 13px;
  color: #4a5568;
  margin-bottom: 6px;
  font-weight: 500;
}

.date-input input {
  width: 100%;
  padding: 12px 16px;
  border: 2px solid #e2e8f0;
  border-radius: 8px;
  font-size: 15px;
  color: #2d3748;
  transition: all 0.2s;
  cursor: pointer;
}

.date-input input:hover {
  border-color: #cbd5e0;
}

.date-input input:focus {
  outline: none;
  border-color: #667eea;
  box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
}

.result {
  background: #f7fafc;
  border-radius: 8px;
  padding: 16px;
  margin-top: 20px;
}

.result-label {
  font-size: 13px;
  color: #718096;
  margin-bottom: 8px;
  font-weight: 500;
}

.result-value {
  font-size: 15px;
  color: #2d3748;
  font-weight: 600;
}

.result-item {
  margin-bottom: 12px;
}

.result-item:last-child {
  margin-bottom: 0;
}

.clear-btn {
  width: 100%;
  padding: 12px;
  background: #667eea;
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
  margin-top: 16px;
}

.clear-btn:hover {
  background: #5568d3;
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(102, 126, 234, 0.4);
}

.clear-btn:active {
  transform: translateY(0);
}

.error {
  border-color: #fc8181 !important;
}

.error-message {
  color: #e53e3e;
  font-size: 13px;
  margin-top: 6px;
}

const startDateInput = document.getElementById('startDate');
const endDateInput = document.getElementById('endDate');
const resultDiv = document.getElementById('result');
const dateRangeSpan = document.getElementById('dateRange');
const totalDaysSpan = document.getElementById('totalDays');
const clearBtn = document.getElementById('clearBtn');
const errorMessage = document.getElementById('errorMessage');

function formatDate(date) {
  const options = { year: 'numeric', month: 'long', day: 'numeric' };
  return date.toLocaleDateString('en-US', options);
}

function calculateDays(start, end) {
  const diff = Math.abs(end - start);
  return Math.ceil(diff / (1000 * 60 * 60 * 24)) + 1;
}

function validateAndUpdate() {
  const startVal = startDateInput.value;
  const endVal = endDateInput.value;

  errorMessage.style.display = 'none';
  startDateInput.classList.remove('error');
  endDateInput.classList.remove('error');

  if (startVal && endVal) {
    const startDate = new Date(startVal);
    const endDate = new Date(endVal);

    if (startDate > endDate) {
      errorMessage.textContent = 'End date must be after start date';
      errorMessage.style.display = 'block';
      endDateInput.classList.add('error');
      resultDiv.style.display = 'none';
      return;
    }

    dateRangeSpan.textContent = `${formatDate(startDate)} - ${formatDate(endDate)}`;
    totalDaysSpan.textContent = `${calculateDays(startDate, endDate)} days`;
    resultDiv.style.display = 'block';
  } else {
    resultDiv.style.display = 'none';
  }
}

startDateInput.addEventListener('change', validateAndUpdate);
endDateInput.addEventListener('change', validateAndUpdate);

clearBtn.addEventListener('click', () => {
  startDateInput.value = '';
  endDateInput.value = '';
  resultDiv.style.display = 'none';
  errorMessage.style.display = 'none';
  startDateInput.classList.remove('error');
  endDateInput.classList.remove('error');
});