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rootulp's solution

to Leap in the JavaScript Track

Published at Jul 13 2018 · 0 comments
Test suite


This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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 ECMAScript to install the necessary dependencies:



Install assignment dependencies:

$ npm install

Making the test suite pass

Execute the tests with:

$ npm test

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing xtest to test.


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.


import Year from './leap';

describe('A leap year', () => {
  test('year not divisible by 4: common year', () => {
    const year = new Year(2015);

  xtest('year divisible by 4, not divisible by 100: leap year', () => {
    const year = new Year(2016);

  xtest('year divisible by 100, not divisible by 400: common year', () => {
    const year = new Year(2100);

  xtest('year divisible by 400: leap year', () => {
    const year = new Year(2000);
class Year {

  constructor(year) {
    this.year = year;

  isLeap() {
    if (this.year % 400 === 0) {
      return true;
    } else if (this.year % 100 === 0) {
      return false;
    } else if (this.year % 4 === 0) {
      return true;
    } else {
      return false;

export default Year;

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