feat(timeDifference): Add timeDifference function (#145)

Author: rigobauer

src/index.js

@@ -50,6 +50,7 @@ import getOrdinalSuffix from './get-ordinal-suffix'
 import arrayAverage from './array-average'
 import find from './find'
 import median from './array-median'
+import timeDifference from './timeDifference'
 
 export {
   isOdd,
@@ -104,4 +105,5 @@ export {
   getOrdinalSuffix,
   arrayAverage,
   median,
+  timeDifference,
 }

src/timeDifference.js

@@ -0,0 +1,29 @@
+export default timeDifference
+
+/**
+* Original Source: https://stackoverflow.com/questions/46883149
+* This method will calculate the time difference
+* between two time values
+*
+* @param {String} startTime - string with the start time in hh:mm format
+* @param {String} endTime - string with the end time in hh:mm format
+* @return {String} - should return a string with the time difference in hh:mm format
+*/
+
+function timeDifference(startTime, endTime) {
+  
+  let hourDiff = ((new Date(`01/01/2018 ${endTime}`)) - (new Date(`01/01/2018 ${startTime}`))) / 60000
+  let hours = 0
+  let minutes = 0
+
+  // If difference is negative, add 24 hours
+  hourDiff = (hourDiff < 0) ? hourDiff + 1440 : hourDiff
+
+  hours = Math.floor(hourDiff / 60)
+  minutes = Math.floor(hourDiff % 60)
+
+  return `${hours < 10 ? `0${hours}` : hours}:${minutes < 10 ? `0${minutes}` : minutes}`
+}
+
+
+

test/timeDifference.test.js

@@ -0,0 +1,18 @@
+import test from 'ava'
+import {timeDifference} from '../src'
+
+test('time difference when startTime<endTime', t => {
+  const startTime = '10:45'
+  const endTime = '19:15'
+  const expected = '08:30'
+  const actual = timeDifference(startTime, endTime)
+  t.is(actual, expected)
+})
+
+test('time difference when startTime>endTime', t => {
+  const startTime = '13:40'
+  const endTime = '09:43'
+  const expected = '20:03'
+  const actual = timeDifference(startTime, endTime)
+  t.is(actual, expected)
+})