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function calculateAge(birthDate) {
 	const today = new Date();
 	const birth = new Date(birthDate);
 	let yearsDiff = today.getFullYear() - birth.getFullYear();
 	let monthsDiff = today.getMonth() - birth.getMonth();
 	let daysDiff = today.getDate() - birth.getDate();
 	// Adjust for negative months or days
 	if (daysDiff < 0) {
 	 	monthsDiff--;
 	 	// Get days in previous month
 	 	const previousMonth = new Date(today.getFullYear(), today.getMonth(), 0);
 	 	daysDiff += previousMonth.getDate();
 	}
 	if (monthsDiff < 0) {
 	 	yearsDiff--;
 	 	monthsDiff += 12;
 	}
 	return {
 	 	years: yearsDiff,
 	 	months: monthsDiff,
 	 	days: daysDiff
 	};
}

function isLeapYear(year) {
 	return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
}
function getDaysInMonth(year, month) {
 	// Month is 0-indexed in JavaScript Date
 	return new Date(year, month + 1, 0).getDate();
}

function calculateDateDifference(startDate, endDate) {
 	const start = new Date(startDate);
 	const end = new Date(endDate);
 	 	if (end < start) {
 	 	// Swap dates if end is before start
 	 	[start, end] = [end, start];
 	}
 	 	let years = end.getFullYear() - start.getFullYear();
 	let months = end.getMonth() - start.getMonth();
 	let days = end.getDate() - start.getDate();
 	 	// Adjust for negative values
 	if (days < 0) {
 	 	months--;
 	 	days += getDaysInMonth(end.getFullYear(), end.getMonth() - 1);
 	}
 	 	if (months < 0) {
 	 	years--;
 	 	months += 12;
 	}
 	 	return { years, months, days };
}

<div class="age-calculator-container">
 	<h2>Age Calculator</h2>
 	<div class="input-section">
 	 	<div class="date-input">
 	 	 	 	<label for="birth-date">Date of Birth:</label>
 	 	 	 	<input type="date" id="birth-date" name="birth-date">
 	 	</div>
 	 	<div class="date-input optional">
 	 	 	 	<label for="calculation-date">Calculate Age on Date (optional):</label>
 	 	 	 	<input type="date" id="calculation-date" name="calculation-date">
 	 	</div>
 	 	<button id="calculate-btn">Calculate Age</button>
 	</div>
 	<div class="results-section">
 	 	<div id="age-result"></div>
 	 	<div id="next-birthday"></div>
 	</div>
</div>

.age-calculator-container {
 	max-width: 600px;
 	margin: 0 auto;
 	padding: 20px;
 	border-radius: 8px;
 	box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
}
.input-section {
 	display: flex;
 	flex-direction: column;
 	gap: 16px;
 	margin-bottom: 24px;
}
.date-input {
 	display: flex;
 	flex-direction: column;
 	gap: 8px;
}
input[type="date"] {
 	padding: 10px;
 	border: 1px solid #ddd;
 	border-radius: 4px;
 	font-size: 16px;
}
button#calculate-btn {
 	padding: 12px 16px;
 	background-color: #4285f4;
 	color: white;
 	border: none;
 	border-radius: 4px;
 	cursor: pointer;
 	font-size: 16px;
 	transition: background-color 0.2s;
}
button#calculate-btn:hover {
 	background-color: #3367d6;
}
.results-section {
 	margin-top: 24px;
 	padding: 16px;
 	background-color: #f9f9f9;
 	border-radius: 4px;
}
/* Responsive adjustments */
@media (max-width: 480px) {
 	.age-calculator-container {
 	 	padding: 15px;
 	}
 	 	input[type="date"] {
 	 	padding: 8px;
 	}
}

document.addEventListener('DOMContentLoaded', () => {
 	const birthDateInput = document.getElementById('birth-date');
 	const calculationDateInput = document.getElementById('calculation-date');
 	const calculateBtn = document.getElementById('calculate-btn');
 	const ageResult = document.getElementById('age-result');
 	const nextBirthdayResult = document.getElementById('next-birthday');
 	 	// Set default max date to today
 	birthDateInput.max = new Date().toISOString().split('T')[0];
 	calculateBtn.addEventListener('click', () => {
 	 	if (!birthDateInput.value) {
 	 	 	 	ageResult.innerHTML = '<p class="error">Please enter a date of birth.</p>';
 	 	 	 	return;
 	 	}
 	 	const birthDate = new Date(birthDateInput.value);
 	 	let referenceDate = new Date();
 	 	 	if (calculationDateInput.value) {
 	 	 	 	referenceDate = new Date(calculationDateInput.value);
 	 	}
 	 	// Calculate age
 	 	const age = calculatePreciseAge(birthDate, referenceDate);
 	 	// Display result
 	 	ageResult.innerHTML = `
 	 	 	 	<h3>Age Result:</h3>
 	 	 	 	<p class="age-display">${age.years} years, ${age.months} months, and ${age.days} days</p>
 	 	 	 	<p class="age-in-days">Total: ${age.totalDays} days</p>
 	 	`;
 	 	// Calculate and display next birthday
 	 	const nextBirthday = calculateNextBirthday(birthDate, referenceDate);
 	 	nextBirthdayResult.innerHTML = `
 	 	 	 	<h3>Next Birthday:</h3>
 	 	 	 	<p>Your next birthday is in ${nextBirthday.months} months and ${nextBirthday.days} days.</p>
 	 	`;
 	});
 	function calculatePreciseAge(birthDate, currentDate) {
 	 	let years = currentDate.getFullYear() - birthDate.getFullYear();
 	 	let months = currentDate.getMonth() - birthDate.getMonth();
 	 	let days = currentDate.getDate() - birthDate.getDate();
 	 	let totalDays = Math.floor((currentDate - birthDate) / (1000 * 60 * 60 * 24));
 	 	// Adjust for negative days
 	 	if (days < 0) {
 	 	 	 	months--;
 	 	 	 	// Get days in the previous month
 	 	 	 	const prevMonthDate = new Date(currentDate.getFullYear(), currentDate.getMonth(), 0);
 	 	 	 	days += prevMonthDate.getDate();
 	 	}
 	 	// Adjust for negative months
 	 	if (months < 0) {
 	 	 	 	years--;
 	 	 	 	months += 12;
 	 	}
 	 	return { years, months, days, totalDays };
 	}
 	 	function calculateNextBirthday(birthDate, currentDate) {
 	 	const nextBirthday = new Date(currentDate.getFullYear(), birthDate.getMonth(), birthDate.getDate());
 	 	// If birthday has passed this year, calculate for next year
 	 	if (nextBirthday < currentDate) {
 	 	 	 	nextBirthday.setFullYear(nextBirthday.getFullYear() + 1);
 	 	}
 	 	const diffTime = nextBirthday - currentDate;
 	 	const diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));
 	 	const months = Math.floor(diffDays / 30);
 	 	const days = diffDays % 30;
 	 	 	return { months, days };
 	}
});

function validateMinimumAge(birthDateString, minimumAge) {
 	const birthDate = new Date(birthDateString);
 	const today = new Date();
 	 	// Calculate age
 	let age = today.getFullYear() - birthDate.getFullYear();
 	const monthDifference = today.getMonth() - birthDate.getMonth();
 	 	// Adjust age if birthday hasn't occurred yet this year
 	if (monthDifference < 0 || (monthDifference === 0 && today.getDate() < birthDate.getDate())) {
 	 	age--;
 	}
 	 	return age >= minimumAge;
}
// Example usage in a form
const registrationForm = document.getElementById('registration-form');
registrationForm.addEventListener('submit', (e) => {
 	const birthDate = document.getElementById('birth-date').value;
 	if (!validateMinimumAge(birthDate, 18)) {
 	 	e.preventDefault();
 	 	alert('You must be at least 18 years old to register.');
 	}
});

function calculateAgeWithTimeZone(birthDateString, timeZone) {
 	// Get current date in specified time zone
 	const options = { timeZone, year: 'numeric', month: 'numeric', day: 'numeric' };
 	const formatter = new Intl.DateTimeFormat('en-US', options);
 	const currentDateParts = formatter.formatToParts(new Date());
 	 	// Extract year, month, day from formatted parts
 	const currentDateObj = currentDateParts.reduce((acc, part) => {
 	 	if (part.type === 'year' || part.type === 'month' || part.type === 'day') {
 	 	 	 	acc[part.type] = parseInt(part.value);
 	 	}
 	 	return acc;
 	}, {});
 	 	// Adjust month (JavaScript months are 0-indexed)
 	currentDateObj.month -= 1;
 	 	const currentDate = new Date(currentDateObj.year, currentDateObj.month, currentDateObj.day);
 	const birthDate = new Date(birthDateString);
 	 	// Calculate age using the time-zone adjusted current date
 	return calculatePreciseAge(birthDate, currentDate);
}

// Using Express.js
const express = require('express');
const app = express();
app.use(express.json());
app.post('/api/calculate-age', (req, res) => {
 	try {
 	 	const { birthDate, referenceDate } = req.body;
 	 	 	if (!birthDate) {
 	 	 	 	return res.status(400).json({ error: 'Birth date is required' });
 	 	}
 	 	 	const birthDateObj = new Date(birthDate);
 	 	const referenceDateObj = referenceDate ? new Date(referenceDate) : new Date();
 	 	 	// Validate dates
 	 	if (isNaN(birthDateObj.getTime())) {
 	 	 	 	return res.status(400).json({ error: 'Invalid birth date format' });
 	 	}
 	 	 	if (isNaN(referenceDateObj.getTime())) {
 	 	 	 	return res.status(400).json({ error: 'Invalid reference date format' });
 	 	}
 	 	 	// Calculate age
 	 	const age = calculatePreciseAge(birthDateObj, referenceDateObj);
 	 	 	res.json({ age });
 	} catch (error) {
 	 	res.status(500).json({ error: 'Server error calculating age' });
 	}
});
app.listen(3000, () => {
 	console.log('Age calculator API running on port 3000');
});

<!-- Accessible date input example -->
<div class="date-input">
 	<label for="birth-date" id="birth-date-label">Date of Birth:</label>
 	<input
 	 	type="date"
 	 	id="birth-date"
 	 	name="birth-date"
 	 	aria-labelledby="birth-date-label"
 	 	aria-describedby="birth-date-format"
 	>
 	<span id="birth-date-format" class="visually-hidden">
 	 	Please enter date in format MM/DD/YYYY
 	</span>
</div>

// Implementing debounce for real-time age calculation
function debounce(func, wait) {
 	let timeout;
 	return function() {
 	 	const context = this;
 	 	const args = arguments;
 	 	clearTimeout(timeout);
 	 	timeout = setTimeout(() => func.apply(context, args), wait);
 	};
}
const debouncedCalculate = debounce(() => {
 	// Age calculation logic
 	calculateAndDisplayAge();
}, 300);
birthDateInput.addEventListener('input', debouncedCalculate);

const moment = require('moment');
function calculateAge(birthdate) {
 	const today = moment();
 	const birthDate = moment(birthdate);
 	 	const years = today.diff(birthDate, 'years');
 	birthDate.add(years, 'years');
 	 	const months = today.diff(birthDate, 'months');
 	birthDate.add(months, 'months');
 	 	const days = today.diff(birthDate, 'days');
 	 	return { years, months, days };
}

import { differenceInYears, differenceInMonths, differenceInDays } from 'date-fns';
function calculateAge(birthdate) {
 	const today = new Date();
 	const birthDate = new Date(birthdate);
 	 	const years = differenceInYears(today, birthDate);
 	const months = differenceInMonths(today, birthDate) % 12;
 	const days = differenceInDays(today, birthDate) % 30; // Approximation
 	 	return { years, months, days };
}

const { DateTime } = require('luxon');
function calculateAge(birthdate) {
 	const today = DateTime.local();
 	const birthDate = DateTime.fromISO(birthdate);
 	 	const diff = today.diff(birthDate, ['years', 'months', 'days']).toObject();
 	 	return {
 	 	years: Math.floor(diff.years),
 	 	months: Math.floor(diff.months),
 	 	days: Math.floor(diff.days)
 	};
}

// Using Jest for testing
describe('Age Calculator Functions', () => {
 	test('Basic age calculation with birthdate in the past', () => {
 	 	// Mock current date to 2023-05-15
 	 	const mockDate = new Date(2023, 4, 15);
 	 	global.Date = jest.fn(() => mockDate);
 	 	 	const birthDate = new Date(1990, 2, 10); // March 10, 1990
 	 	const age = calculateAge(birthDate);
 	 	 	expect(age.years).toBe(33);
 	 	expect(age.months).toBe(2);
 	 	expect(age.days).toBe(5);
 	});
 	 	test('Age calculation with future reference date', () => {
 	 	const birthDate = new Date(2000, 0, 1); // January 1, 2000
 	 	const referenceDate = new Date(2030, 6, 15); // July 15, 2030
 	 	 	const age = calculateAgeBetweenDates(birthDate, referenceDate);
 	 	 	expect(age.years).toBe(30);
 	 	expect(age.months).toBe(6);
 	 	expect(age.days).toBe(14);
 	});
 	 	test('Edge case: Birth date is February 29 on leap year', () => {
 	 	const birthDate = new Date(2000, 1, 29); // February 29, 2000
 	 	const referenceDate = new Date(2023, 2, 1); // March 1, 2023
 	 	 	const age = calculateAgeBetweenDates(birthDate, referenceDate);
 	 	 	expect(age.years).toBe(23);
 	 	expect(age.months).toBe(0);
 	 	expect(age.days).toBe(1);
 	});
});

function calculatePatientAgeDetails(dateOfBirth) {
 	const age = calculatePreciseAge(new Date(dateOfBirth), new Date());
 	 	// Determine age category for medical protocols
 	let ageCategory;
 	if (age.years < 2) {
 	 	ageCategory = 'infant';
 	} else if (age.years < 13) {
 	 	ageCategory = 'child';
 	} else if (age.years < 18) {
 	 	ageCategory = 'adolescent';
 	} else if (age.years < 65) {
 	 	ageCategory = 'adult';
 	} else {
 	 	ageCategory = 'senior';
 	}
 	 	// Calculate age in months for young children
 	const totalMonths = age.years * 12 + age.months;
 	 	return {
 	 	...age,
 	 	ageCategory,
 	 	totalMonths,
 	 	// Include whether special protocols apply
 	 	requiresPediatricProtocol: age.years < 18,
 	 	requiresGeriatricProtocol: age.years >= 65
 	};
}

function verifyPurchaseEligibility(dateOfBirth, productMinimumAge) {
 	const today = new Date();
 	const birthDate = new Date(dateOfBirth);
 	 	// Calculate age as of today
 	let age = today.getFullYear() - birthDate.getFullYear();
 	 	// Adjust age if birthday hasn't occurred yet this year
 	if (
 	 	today.getMonth() < birthDate.getMonth() ||
 	 	(today.getMonth() === birthDate.getMonth() && today.getDate() < birthDate.getDate())
 	) {
 	 	age--;
 	}
 	 	return {
 	 	eligible: age >= productMinimumAge,
 	 	currentAge: age,
 	 	minimumAge: productMinimumAge,
 	 	// Calculate days until eligibility if not eligible
 	 	daysUntilEligible: age < productMinimumAge ?
 	 	 	 	calculateDaysUntilEligible(birthDate, productMinimumAge) : 0
 	};
}
function calculateDaysUntilEligible(birthDate, requiredAge) {
 	const today = new Date();
 	const eligibilityDate = new Date(birthDate);
 	 	eligibilityDate.setFullYear(birthDate.getFullYear() + requiredAge);
 	 	// If eligibility date has passed this year, calculate for next year
 	if (eligibilityDate < today) {
 	 	return 0;
 	}
 	 	const diffTime = Math.abs(eligibilityDate - today);
 	return Math.ceil(diffTime / (1000 * 60 * 60 * 24));
}