给一个指定日期date,往前推days天
function getBeforeDateForDays(date,days){
var date = days.split('-');var newDate = new Date(date[0], date[1]-1, date[2]);
var year,month,day;
newDate.setDate(newDate.getDate() - days); // + day 就是往前推day天
year = newDate.getFullYear();
month = newDate.getMonth() + 1;
day = newDate.getDate() ;
var afterDay = year + '-' + ( month < 10 ? ( '0' + month ) : month ) + '-' + ( day < 10 ? ( '0' + day ) : day) ;
return afterDay;
}