diff --git a/Conversions/DateToDay.js b/Conversions/DateToDay.js
index 8683bdec4b..4086e4688b 100644
--- a/Conversions/DateToDay.js
+++ b/Conversions/DateToDay.js
@@ -39,22 +39,30 @@ const daysNameList = { // weeks-day
 6: 'Saturday'
 }
 
+// javascript n % m is the remainder operator which is different than modulus operator
+// https://stackoverflow.com/questions/4467539/javascript-modulo-gives-a-negative-result-for-negative-numbers
+const mod = (n, m) => {
+ return ((n % m) + m) % m
+}
+
 const DateToDay = (date) => {
 // firstly, check that input is a string or not.
 if (typeof date !== 'string') {
 return new TypeError('Argument is not a string.')
 }
 // extract the date
- const [day, month, year] = date.split('/').map((x) => Number(x))
+ let [day, month, year] = date.split('/').map((x) => Number(x))
 // check the data are valid or not.
 if (day < 0 &#124;&#124; day> 31 &#124;&#124; month> 12 &#124;&#124; month < 0) { return new TypeError('Date is not valid.') } + // adjust year since Jan & Feb are considered from previous year + if (month < 3) year-- // divide year to century and yearDigit value. - const yearDigit = (year % 100) const century = Math.floor(year / 100) + const yearDigit = (year - century * 100) // Apply the algorithm shown above - const weekDay = Math.abs((day + Math.floor((2.6 * calcMonthList[month]) - 0.2) - (2 * century) + yearDigit + Math.floor(yearDigit / 4) + Math.floor(century / 4)) % 7) + const weekDay = mod(day + Math.floor((2.6 * calcMonthList[month]) - 0.2) - (2 * century) + yearDigit + Math.floor(yearDigit / 4) + Math.floor(century / 4), 7) // return the weekDay name. return daysNameList[weekDay] } diff --git a/Conversions/test/DateToDay.test.js b/Conversions/test/DateToDay.test.js index a932dff08c..1b19a6b8a1 100644 --- a/Conversions/test/DateToDay.test.js +++ b/Conversions/test/DateToDay.test.js @@ -1,8 +1,8 @@ import { DateToDay } from '../DateToDay' -test('The date 18/02/2001 is Monday', () => {
+test('The date 18/02/2001 is Sunday', () => {
 const res = DateToDay('18/02/2001')
- expect(res).toBe('Monday')
+ expect(res).toBe('Sunday')
 })
 
 test('The date 18/12/2020 is Friday', () => {
@@ -14,7 +14,18 @@ test('The date 12/12/2012 is Wednesday', () => {
 const res = DateToDay('12/12/2012')
 expect(res).toBe('Wednesday')
 })
-test('The date 01/01/2001 is Friday', () => {
+
+test('The date 01/01/2001 is Monday', () => {
 const res = DateToDay('01/01/2001')
- expect(res).toBe('Friday')
+ expect(res).toBe('Monday')
+})
+
+test('The date 01/01/2020 is Wednesday', () => {
+ const res = DateToDay('01/01/2020')
+ expect(res).toBe('Wednesday')
+})
+
+test('The date 01/01/1900 is Monday', () => {
+ const res = DateToDay('01/01/1900')
+ expect(res).toBe('Monday')
 })
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