Leap Year Check in JavaScript

1// Leap year rules:
2// 1. Divisible by 4 → Leap year
3// 2. BUT if divisible by 100 → NOT leap year
4// 3. UNLESS divisible by 400 → Leap year
5
6function isLeapYear(year) {
7    if (year % 400 === 0) {
8        return true;
9    } else if (year % 100 === 0) {
10        return false;
11    } else if (year % 4 === 0) {
12        return true;
13    } else {
14        return false;
15    }
16}
17
18// Test cases
19console.log("2000:", isLeapYear(2000) ? "Leap year" : "Not leap year");
20console.log("1900:", isLeapYear(1900) ? "Leap year" : "Not leap year");
21console.log("2024:", isLeapYear(2024) ? "Leap year" : "Not leap year");
22console.log("2023:", isLeapYear(2023) ? "Leap year" : "Not leap year");
23
24// Method 2: Single expression
25function isLeapYear2(year) {
26    return (year % 400 === 0) || (year % 4 === 0 && year % 100 !== 0);
27}
28
29console.log("\nUsing single expression:");
30console.log("2000:", isLeapYear2(2000));
31console.log("1900:", isLeapYear2(1900));
32console.log("2024:", isLeapYear2(2024));
33
34// Method 3: Using ternary
35function isLeapYear3(year) {
36    return year % 400 === 0 ? true : 
37           year % 100 === 0 ? false : 
38           year % 4 === 0 ? true : false;
39}
40
41console.log("\nUsing ternary:");
42console.log("2000:", isLeapYear3(2000));
43console.log("2023:", isLeapYear3(2023));