如何在 JAVASCRIPT 中实现 MS-excel 的 EDATE() 功能

Question

i have to implement EDATE functionality of MS-Excel into JAVASCRIPT

sample:

EDATE(06-Aug-2020,13)

Result: 06-Sept-2021

Answer 1

There is no such functionality, you have to build it by yourself.

First I generate from your string a JS-date. From this I extract year, month and day.
Than I sum the extramonths up and get the month by modulu 12 (months in JS are counted 0-11). If the months are negative I add 12 months up. For the year I add the integer part from monthSum didide through 12.
If the day is greater or equal 29 and it's February and it's Leap year (year modulo 4 is 0) than the day is setted to 29. In all other cases the day is setted ton the minimum of privious day and the maximum of days in this month (stored in array MONTH).
Now I have the desired date and I only format it for return: For getting the day with 2-digit add before the string "0" and then take the last 2 chars. For the abbreviation from the month I use the array MONTH.

Try it out. I give you some critical examples with the Leap day and with negative/positive months which produces yearchange.

 function edate(dateString, monthExtra) { const DAYS = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]; const MONTH = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']; let date = new Date(dateString); let year= -date.getFullYear(); let month = date.getMonth(); let day = date.getDate(); let monthSum = month + monthExtra; month = monthSum %12; if (month < 0) { month = 12 + month; } year = year + Math.floor(monthSum/12); if ( day>=29 && month==1 && (year %4 == 0 )) { day = 29; } else { day = Math.min(day, DAYS[month]); } return ("0" + day).slice(-2) + '-' + MONTH[month] + '-' + year; } console.log(edate('06-Aug-2020', 13)); console.log(edate('30-Jan-2020', -13)); console.log(edate('30-Jan-2019', 1)); console.log(edate('29-Mar-2020', -13));