js控制两个日期相减

function getOffDays(startDate, endDate){
var startDateArr = startDate.split("-");
var checkStartDate = new Date();
checkStartDate.setFullYear(startDateArr[0], startDateArr[1], startDateArr[2]);
var endDateArr = endDate.split("-");
var checkEndDate = new Date();
checkEndDate.setFullYear(endDateArr[0], endDateArr[1], endDateArr[2]);
var mmSec = (checkEndDate.getTime() - checkStartDate.getTime())/ 3600000 / 24;
if(startDateArr[0]!=endDateArr[0]){
flag = true;
}
return mmSec;
}

这里的日期类型是带-的，如2017-05-05