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# n0mn0m's solution

## to Leap in the TypeScript Track

Published at Nov 07 2020 · 0 comments
Instructions
Test suite
Solution

#### Note:

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.

## 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:

https://exercism.io/tracks/typescript/installation

## Requirements

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`.

## 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): boolean {
return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
}

export default isLeapYear``````