日期的格式：

var date1 = 2021/3/1;
var date2 = 2021/3/31;
var f = DateDiff(date1,date2);
function DateDiff(date1, date2) {
            var f;
            var aDate1 = new Date(date1);
            var aDate2 = new Date(date2);
            f = oDate1 - oDate2;
            return f;
        }