# chrisman's solution

## to Raindrops in the JavaScript Track

Published at Jul 13 2018 · 1 comment
Instructions
Test suite
Solution

#### Note:

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.

Convert a number to a string, the contents of which depend on the number's factors.

• If the number has 3 as a factor, output 'Pling'.
• If the number has 5 as a factor, output 'Plang'.
• If the number has 7 as a factor, output 'Plong'.
• If the number does not have 3, 5, or 7 as a factor, just pass the number's digits straight through.

## Examples

• 28's factors are 1, 2, 4, 7, 14, 28.
• In raindrop-speak, this would be a simple "Plong".
• 30's factors are 1, 2, 3, 5, 6, 10, 15, 30.
• In raindrop-speak, this would be a "PlingPlang".
• 34 has four factors: 1, 2, 17, and 34.
• In raindrop-speak, this would be "34".

## Setup

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

http://exercism.io/languages/javascript/installation

## Running the test suite

The provided test suite uses Jasmine. You can install it by opening a terminal window and running the following command:

``````npm install -g jasmine
``````

Run the test suite from the exercise directory with:

``````jasmine raindrops.spec.js
``````

In many test suites all but the first test have been marked "pending". Once you get a test passing, activate the next one by changing `xit` to `it`.

## Source

A variation on a famous interview question intended to weed out potential candidates. http://jumpstartlab.com

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### raindrops.spec.js

``````var Raindrops = require('./raindrops');

describe('Raindrops', function () {
var drops = new Raindrops();

it('converts 1', function () {
expect(drops.convert(1)).toEqual('1');
});

xit('converts 3', function () {
expect(drops.convert(3)).toEqual('Pling');
});

xit('converts 5', function () {
expect(drops.convert(5)).toEqual('Plang');
});

xit('converts 7', function () {
expect(drops.convert(7)).toEqual('Plong');
});

xit('converts 6', function () {
expect(drops.convert(6)).toEqual('Pling');
});

xit('converts 9', function () {
expect(drops.convert(9)).toEqual('Pling');
});

xit('converts 10', function () {
expect(drops.convert(10)).toEqual('Plang');
});

xit('converts 14', function () {
expect(drops.convert(14)).toEqual('Plong');
});

xit('converts 15', function () {
expect(drops.convert(15)).toEqual('PlingPlang');
});

xit('converts 21', function () {
expect(drops.convert(21)).toEqual('PlingPlong');
});

xit('converts 25', function () {
expect(drops.convert(25)).toEqual('Plang');
});

xit('converts 35', function () {
expect(drops.convert(35)).toEqual('PlangPlong');
});

xit('converts 49', function () {
expect(drops.convert(49)).toEqual('Plong');
});

xit('converts 52', function () {
expect(drops.convert(52)).toEqual('52');
});

xit('converts 105', function () {
expect(drops.convert(105)).toEqual('PlingPlangPlong');
});

xit('converts 12121', function () {
expect(drops.convert(12121)).toEqual('12121');
});
});``````
``````'use strict'

var Left = function(x) {
this.__value = x;
};

Left.of = function(x) {
return new Left(x);
}

Left.prototype.map = function(f) {
return this; // do not map
}

var Right = function(x) {
this.__value = x;
};

Right.of = function(x) {
return new Right(x);
}

Right.prototype.map = function(f) {
return new Right.of(f(this.__value));
}

var map = (f) => (x) => x.map(f);

var id = (x) => x;

var compose = (...fs) => (init) =>
fs.reduceRight((val, f) => f(val), init);

// factor :: num => num => boolean
var factor = (factor) => (num) => num % factor === 0;

var either = (f, g) => (e) => {
switch (e.constructor) {
case Left:
return f(e.__value);
case Right:
return g(e.__value);
}
}

var string = (num) => num.toString();

var log = (msg) => (x) => {
console.log(msg, x);
return x;
}

// getFactors :: number => either(number, string)
var getFactors = (num) => {
var res
= (factor(3)(num) ? 'Pling' : '')
+ (factor(5)(num) ? 'Plang' : '')
+ (factor(7)(num) ? 'Plong' : '')
;

// no factors is treated as an error
return (res.length === 0)
? Left.of(num)
: Right.of(res);
};

class Raindrops {
convert(num) {
return compose(
either(string, id), getFactors
)(num);
}
}

module.exports = Raindrops;``````

chrisman
Solution Author
commented almost 5 years ago

first time trying to implement some functional error handling via Left, Right, and either.

### What can you learn from this solution?

A huge amount can be learned from reading other peopleโ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?