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to Leap (Legacy) in the JavaScript Track

Test suite


Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

on every year that is evenly divisible by 4
  except every year that is evenly divisible by 100
    unless the year is also evenly divisible by 400

For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.

If your language provides a method in the standard library that does this look-up, pretend it doesn't exist and implement it yourself.


Though our exercise adopts some very simple rules, there is more to learn!

For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.


Go through the setup instructions for JavaScript to install the necessary dependencies:


Running the test suite

The provided test suite uses Jasmine. You can install it by opening a terminal window and running the following command:

npm install -g jasmine

Run the test suite from the exercise directory with:

jasmine leap.spec.js

In many test suites all but the first test have been marked "pending". Once you get a test passing, activate the next one by changing xit to it.


JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


var Year = require('./leap');

describe('Leap year', function () {
  it('is not very common', function () {
    var year = new Year(2015);

  xit('is introduced every 4 years to adjust about a day', function () {
    var year = new Year(2016);

  xit('is skipped every 100 years to remove an extra day', function () {
    var year = new Year(1900);

  xit('is reintroduced every 400 years to adjust another day', function () {
    var year = new Year(2000);

  // Feel free to enable the following tests to check some more examples
  xdescribe('Additional example of a leap year that', function () {
    it('is not a leap year', function () {
      var year = new Year(1978);

    it('is a common leap year', function () {
      var year = new Year(1992);

    it('is skipped every 100 years', function () {
      var year = new Year(2100);

    it('is reintroduced every 400 years', function () {
      var year = new Year(2400);
module.exports = 

class Year {
  constructor(year) {
    const divisible = x => year % x == 0
    this.leap = divisible(4) && (!divisible(100) || divisible(400))
  isLeap() {
    return this.leap

What can you learn from this solution?

A huge amount can be learnt from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that I could read more about to develop my understanding?