Calculate Age in JavaScript

1// Method 1: Simple age calculation
2function calculateAge(birthDate) {
3    const today = new Date();
4    let age = today.getFullYear() - birthDate.getFullYear();
5    const monthDiff = today.getMonth() - birthDate.getMonth();
6    
7    if (monthDiff < 0 || (monthDiff === 0 && today.getDate() < birthDate.getDate())) {
8        age--;
9    }
10    
11    return age;
12}
13
14const birthDate = new Date('1990-05-15');
15console.log('Age:', calculateAge(birthDate));
16
17// Method 2: Age with months and days
18function calculateAgeDetailed(birthDate) {
19    const today = new Date();
20    let years = today.getFullYear() - birthDate.getFullYear();
21    let months = today.getMonth() - birthDate.getMonth();
22    let days = today.getDate() - birthDate.getDate();
23    
24    if (days < 0) {
25        months--;
26        const lastMonth = new Date(today.getFullYear(), today.getMonth(), 0);
27        days += lastMonth.getDate();
28    }
29    
30    if (months < 0) {
31        years--;
32        months += 12;
33    }
34    
35    return { years, months, days };
36}
37
38const ageDetailed = calculateAgeDetailed(birthDate);
39console.log(`${ageDetailed.years} years, ${ageDetailed.months} months, ${ageDetailed.days} days`);
40
41// Method 3: Age in different units
42function ageInUnits(birthDate) {
43    const today = new Date();
44    const diff = today - birthDate;
45    
46    return {
47        milliseconds: diff,
48        seconds: Math.floor(diff / 1000),
49        minutes: Math.floor(diff / (1000 * 60)),
50        hours: Math.floor(diff / (1000 * 60 * 60)),
51        days: Math.floor(diff / (1000 * 60 * 60 * 24)),
52        weeks: Math.floor(diff / (1000 * 60 * 60 * 24 * 7)),
53        months: Math.floor(diff / (1000 * 60 * 60 * 24 * 30.44)),
54        years: Math.floor(diff / (1000 * 60 * 60 * 24 * 365.25))
55    };
56}
57
58const ageUnits = ageInUnits(birthDate);
59console.log('Age in units:', ageUnits);
60
61// Method 4: Next birthday
62function getNextBirthday(birthDate) {
63    const today = new Date();
64    const currentYear = today.getFullYear();
65    let nextBirthday = new Date(currentYear, birthDate.getMonth(), birthDate.getDate());
66    
67    if (nextBirthday < today) {
68        nextBirthday.setFullYear(currentYear + 1);
69    }
70    
71    return nextBirthday;
72}
73
74const nextBirthday = getNextBirthday(birthDate);
75console.log('Next birthday:', nextBirthday);
76
77// Method 5: Days until birthday
78function daysUntilBirthday(birthDate) {
79    const nextBirthday = getNextBirthday(birthDate);
80    const today = new Date();
81    const diff = nextBirthday - today;
82    return Math.ceil(diff / (1000 * 60 * 60 * 24));
83}
84
85console.log('Days until birthday:', daysUntilBirthday(birthDate));