JavaScript/Conversions/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 }