add DateToDay method withour Date class

suryapratapsinghsuryavanshi · suryapratapsinghsuryavanshi · commit 766d35c2e956 · 2021-08-23T12:28:17.000+05:30
diff --git a/Conversions/DateToDay.js b/Conversions/DateToDay.js
@@ -0,0 +1,64 @@
+/*
+                    DateToDay Method
+                    ----------------
+    The DateToDay method takes a date in string format and 
+    returns the name of a day. The approach behind this method 
+    is very simple, we first take a string date and check 
+    whether their date is valid or not, if the date is valid 
+    then we do this But apply the algorithm shown below. The 
+    algorithm shown below gives us the number of the day and 
+    finally converts it to the name of the day.
+
+    Algorithm & Explanation : https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html
+*/
+
+// March is taken as the first month of the year.
+const calcMonthList = {
+    1: 11,
+    2: 12,
+    3: 1,
+    4: 2,
+    5: 3,
+    6: 4,
+    7: 5,
+    8: 6,
+    9: 7,
+    10: 8,
+    11: 9,
+    12: 10
+}
+
+// show the week day in a number : Sunday - Saturday => 0 - 6
+const daysNameList = { // weeks-day
+  0: 'Sunday',
+  1: 'Monday',
+  2: 'Tuesday',
+  3: 'Wednesday',
+  4: 'Thursday',
+  5: 'Friday',
+  6: 'Saturday'
+}
+
+const DateToDay = (date) => {
+  // firstly, check that input is a string or not.
+  if (typeof date !== 'string') {
+    return new TypeError('Argument is not a string.')
+  }
+  // extarct the date
+  const [day, month, year] = date.split('/').map((x) => Number(x))
+  // check the data are valid or not.
+  if ( day < 0 || day > 31 || month > 12 || month < 0) {
+    return new TypeError('Date is not valid.')
+  }
+  // divide year to century and yearDigit value.
+  const yearDigit = (year % 100)
+  const century = Math.floor(year / 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)
+  // return the weekDay name.
+  return daysNameList[weekDay];
+}
+
+// Example : DateToDay("18/12/2020") => Friday
+
+module.exports = DateToDay
