# atmantree's solution

## to Leap in the TypeScript Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

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.

## Notes

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.

## Setup

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

http://exercism.io/languages/typescript

## Requirements

Install assignment dependencies:

``````\$ yarn install
``````

## Making the test suite pass

Execute the tests with:

``````\$ yarn test
``````

## Source

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.

### leap.test.ts

``````import isLeapYear from './leap'

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

it('is not very common', () => {
expect(isLeapYear(2015)).toBeFalsy()
})

xit('is introduced every 4 years to adjust about a day', () => {
expect(isLeapYear(2016)).toBeTruthy()
})

xit('is skipped every 100 years to remove an extra day', () => {
expect(isLeapYear(1900)).toBeFalsy()
})

xit('is reintroduced every 400 years to adjust another day', () => {
expect(isLeapYear(2000)).toBeTruthy()
})

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

xit('is not a leap year', () => {
expect(isLeapYear(1978)).toBeFalsy()
})

xit('is a common leap year', () => {
expect(isLeapYear(1992)).toBeTruthy()
})

xit('is skipped every 100 years', () => {
expect(isLeapYear(2100)).toBeFalsy()
})

xit('is reintroduced every 400 years', () => {
expect(isLeapYear(2400)).toBeTruthy()
})
})
})``````
``````function isLeapYear( year: number ) {
if (year % 400 == 0) return true
if (year % 100 == 0) return false
if (year %   4 == 0) return true
return false
}

export default isLeapYear``````