JavaScript Program to Check if a Given Year is Leap Year

In this article, we will see how to write a JavaScript program to check if a given year is a leap year. Leap year must satisfy the following conditions:

• The year is multiple of 400.
• The year is a multiple of 4 and not a multiple of 100.

Below are the approaches:

Approach 1: Traditional Leap Year Logic

Our approach will be to verify the leap-year conditions mentioned above.

• First, Check the given input year is a multiple of 400. If true give output “Input year is a Leap year”.
• If false, Check for the secondary conditions that the input year must be a multiple of 4 but not 100.
• Then display the output accordingly.

Example 1: In this example, we will check the conditions of Leap year for previous years

Javascript

function isLeapYear(year) {
    if (
        year % 100 === 0 ? year % 400 === 0 : year % 4 === 0
    )
        console.log(" Input year:", year, "is a Leap Year");
    else
        console.log(
            " Input year:",
            year,
            "is NOT a Leap Year"
        );
}

let inputYear = 2020;
isLeapYear(inputYear);
inputYear = 2023;
isLeapYear(inputYear);

Output

 Input year: 2020 is a Leap Year
 Input year: 2023 is NOT a Leap Year

Example 2: In this example, we will check the conditions of Leap year for next/ upcoming years

Javascript

function isLeapYear(year) {
    if (
        year % 100 === 0 ? year % 400 === 0 : year % 4 === 0
    )
        console.log(" Input year:", year, "is a Leap Year");
    else
        console.log(
            " Input year:",
            year,
            "is NOT a Leap Year"
        );
}

let inputYear = 2354;
isLeapYear(inputYear);
inputYear = 2640;
isLeapYear(inputYear);

Output

 Input year: 2354 is NOT a Leap Year
 Input year: 2640 is a Leap Year

Approach 2: Using newDate()

• A Date object is created with the given year, month (1 for February), and day (29).
• The getMonth() method returns the month (0-indexed), and getDate() returns the day of the month.
• If the month is still February, and the day is 29, then it is a leap year.

Example: In this example, we are using newDate().

Javascript

function isLeapYearUsingDate(year) {
// Create a new date on February 29th of the given year
let leapDate = new Date(year, 1, 29);

// Check if the month is still February and the date is 29
return leapDate.getMonth() === 1 && leapDate.getDate() === 29;
}

// Example usage:
let yearToCheck = 2024;
let result = isLeapYearUsingDate(yearToCheck);

console.log(result ? yearToCheck + " is a leap year." : yearToCheck + " is not a leap year.");

Output

2024 is a leap year.