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4d47's solution

to Leap (Legacy) in the JavaScript Track

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Instructions
Test suite
Solution

Leap

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 Javascript to install the necessary dependencies:

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

Requirements

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.

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.spec.js

import { isLeap } from './leap';

describe('A leap year', () => {
  test('year not divisible by 4: common year', () => {
    expect(isLeap(2015)).toBeFalsy();
  });

  xtest('year divisible by 4, not divisible by 100: leap year', () => {
    expect(isLeap(2016)).toBeTruthy();
  });

  xtest('year divisible by 100, not divisible by 400: common year', () => {
    expect(isLeap(2100)).toBeFalsy();
  });

  xtest('year divisible by 400: leap year', () => {
    expect(isLeap(2000)).toBeTruthy();
  });
});
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?