DateDayDifference.js

/*
 DateDayDifference Method
 ------------------------
 DateDayDifference method calculates the number of days between two dates.

 Algorithm & Explanation : https://ncalculators.com/time-date/date-difference-calculator.htm
*/

// Internal method for make calculations easier
const isLeap = (year) => {
 if (year % 400 === 0) return true
 else if (year % 100 === 0) return false
 else if (year % 4 === 0) return true
 else return false
}
const DateToDay = (dd, mm, yyyy) => {
 return Math.floor(
 365 * (yyyy - 1) +
 (yyyy - 1) / 4 -
 (yyyy - 1) / 100 +
 (yyyy - 1) / 400 +
 dd +
 (367 * mm - 362) / 12 +
 (mm <= 2 ? 0 : isLeap(yyyy) ? -1 : -2)
 )
}

const DateDayDifference = (date1, date2) => {
 // firstly, check that both input are string or not.
 if (typeof date1 !== 'string' || typeof date2 !== 'string') {
 return new TypeError('Argument is not a string.')
 }
 // extract the first date
 const [firstDateDay, firstDateMonth, firstDateYear] = date1
 .split('/')
 .map((ele) => Number(ele))
 // extract the second date
 const [secondDateDay, secondDateMonth, secondDateYear] = date2
 .split('/')
 .map((ele) => Number(ele))
 // check the both data are valid or not.
 if (
 firstDateDay < 0 ||
 firstDateDay > 31 ||
 firstDateMonth > 12 ||
 firstDateMonth < 0 ||
 secondDateDay < 0 ||
 secondDateDay > 31 ||
 secondDateMonth > 12 ||
 secondDateMonth < 0
 ) {
 return new TypeError('Date is not valid.')
 }
 return Math.abs(
 DateToDay(secondDateDay, secondDateMonth, secondDateYear) -
 DateToDay(firstDateDay, firstDateMonth, firstDateYear)
 )
}

// Example : DateDayDifference('17/08/2002', '10/10/2020') => 6630

export { DateDayDifference }