Check a leap year

Apply the Gregorian divisible-by-4, century and 400-year rules.

JavaScript Version 1.0.0 · MIT · .md

function isLeapYear(year) { return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0); }

Try in the local lab Download function

Input & expected output

Input

Expected output

true

The edge case

Input

Expected output

false

Know the limits

Input is an integer year from 1 to 9,999 in the proleptic Gregorian calendar.

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Source & maintenance

Curated implementation; explicit input bounds, edge cases, local fixtures and rebuilt presentation. Original MDX retained as inert source evidence.

Maintained by Oveyon. Source commit: 14b481cf60df. Read the license.

Local fixture scope · Node.js 22.23.2 · reviewed October 28, 2026. No external service is required.

Keep exploring

Check whether all values are equal — Compare every item with the first using Object.is.
Check whether an object is empty — Check for own enumerable string keys on a JSON object.
Check whether an integer is even — Test parity for safe integers, including zero and negative values.