Get days difference between dates (獲取兩個日期間的差距)
計算兩個 Date對象之間的差距(以天為單位)。
const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24);
// getDaysDiffBetweenDates(new Date("2017-12-13"), new Date("2017-12-22")) -> 9