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n0mn0m's solution

to Leap in the TypeScript Track

Published at Nov 07 2020 · 0 comments
Test suite


This exercise has changed since this solution 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.


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 TypeScript to install the necessary dependencies:



Install assignment dependencies:

$ yarn install

Making the test suite pass

Execute the tests with:

$ yarn 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 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.


import isLeapYear from './leap'

describe('A leap year', () => {

  it('is not very common', () => {

  xit('is introduced every 4 years to adjust about a day', () => {

  xit('is skipped every 100 years to remove an extra day', () => {

  xit('is reintroduced every 400 years to adjust another day', () => {

  describe('Additional example of a leap year that', () => {

    xit('is not a leap year', () => {

    xit('is a common leap year', () => {

    xit('is skipped every 100 years', () => {

    xit('is reintroduced every 400 years', () => {
function isLeapYear(year: number): boolean {
    return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);

export default isLeapYear

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