new Date getMonth

Leap
Leap in JavaScript 
export function isLeap(year) {
  return new Date(year, 1, 29).getMonth() == 1;
}
Caution

This approach may be considered a "cheat" for this exercise.

By creating a new Date from February 29th for the year, you can see if the month is still February. If it is, then the year is a leap year. This is checked by using the getMonth method of the Date object.

Note

Note that the value returned from the getMonth method is zero-based, meaning that February is 1, not 2.

Shortening

When the body of a function is a single expression, the function can be implemented as an arrow function, like so

export const isLeap = (year) => new Date(year, 1, 29).getMonth() == 1;

Notice that return and the curly braces are not needed.

15th May 2024 · Found it useful?

Other Approaches to Leap in JavaScript

Other ways our community solved this exercise
export function isLeap(year) {
  return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
Boolean chain

Use a chain of boolean expressions. 

export function isLeap(year) {
  return year % 100 == 0 ? year % 400 == 0 : year % 4 == 0;
}
Ternary operator

Use a ternary operator of boolean expressions. 

switch (true) {
  case year % 400 == 0:
    return true;
  case year % 100 == 0:
    return false;
  default:
    return year % 4 == 0;
}
switch statement

Use a switch statement.