JS: Calculate percentage difference

Add feature to changelog and description to readme.

changelog.md

@@ -16,5 +16,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-[unreleased]: https://github.com/rodrigobdz/percentage-diff/compare
-<!-- Example: https://github.com/rodrigobdz/percentage-diff/compare/v1.0.0...HEAD -->
+## [1.0.0] - 2019-04-24
+
+### Added
+
+- Calculate percentage difference between two numbers.
+
+[unreleased]: https://github.com/rodrigobdz/percentage-diff/compare/v1.0.0...HEAD
+[1.0.0]: https://github.com/rodrigobdz/percentage-diff/compare/839407f777811173c2bbb62af850e3fc6ee07ebf...v1.0.0

index.js

@@ -1,9 +1,15 @@
 'use strict';
 
-module.exports = (input, options = {}) => {
-	if (typeof input !== 'string') {
-		throw new TypeError(`Expected a string, got ${typeof input}`);
+module.exports = (firstNr, secondNr) => {
+	if (typeof firstNr !== 'number') {
+		throw new TypeError(`Expected a number, got ${typeof firstNr}`);
 	}
 
-	return input + ' & ' + (options.postfix || 'rainbows');
+	if (typeof secondNr !== 'number') {
+		throw new TypeError(`Expected a number, got ${typeof secondNr}`);
+	}
+
+	const percentageDiff = (secondNr - firstNr) / firstNr * 100;
+
+	return Number(percentageDiff.toFixed(2));
 };

readme.md

@@ -13,30 +13,23 @@ $ npm install percentage-diff
 ```js
 const percentageDiff = require('percentage-diff');
 
-percentageDiff('unicorns');
-//=> 'unicorns & rainbows'
+percentageDiff(50, 75);
+//=> 50%
+percentageDiff(45,35);
+//=> -22.22%
 ```
 
 ## API
 
-### percentageDiff(input, [options])
+### percentageDiff(firstNr, secondNr)
 
-#### input
+#### firstNr
 
-Type: `string`
+Type: `number`
 
-Lorem ipsum.
+#### secondNr
 
-#### options
-
-Type: `Object`
-
-##### foo
-
-Type: `boolean`<br>
-Default: `false`
-
-Lorem ipsum.
+Type: `number`
 
 ## Credits
 

test.js

@@ -1,11 +1,36 @@
 import test from 'ava';
 import percentageDiff from '.';
 
-test('title', t => {
-	const err = t.throws(() => {
-		percentageDiff(123);
+test('Validate argument types', t => {
+	const err1 = t.throws(() => {
+		percentageDiff('123', 12);
 	}, TypeError);
-	t.is(err.message, 'Expected a string, got number');
+	t.is(err1.message, 'Expected a number, got string');
+	const err2 = t.throws(() => {
+		percentageDiff(123, '12');
+	}, TypeError);
+	t.is(err2.message, 'Expected a number, got string');
+});
+
+test('First number is larger than second one', t => {
+	t.is(percentageDiff(3595210, 738583), -79.46);
+	t.is(percentageDiff(75, 50), -33.33);
+	t.is(percentageDiff(45, 35), -22.22);
+});
+
+test('Second number is larger than first one', t => {
+	t.is(percentageDiff(12, 32), 166.67);
+	t.is(percentageDiff(27, 96), 255.56);
+	t.is(percentageDiff(50, 75), 50);
+	t.is(percentageDiff(35, 45), 28.57);
+});
+
+test('Both numbers are equal', t => {
+	t.is(percentageDiff(12, 12), 0);
+	t.is(percentageDiff(-5, -5.0), 0);
+});
 
-	t.is(percentageDiff('unicorns'), 'unicorns & rainbows');
+test('Handles zero division', t => {
+	t.is(percentageDiff(0, 0), NaN);
+	t.is(percentageDiff(0, 2), Infinity);
 });