加减天数之后等到的时间

//date加上num天数之后等到的时间;date格式：YYYY-MM-DD
function changeDate(date,num){
var dates = date.split("-");
if(dates.length != 3){
  alert("时间格式错误，请确认!");
  return ;
}
var newDate = new Date(dates[0],Number(dates[1])-1,Number(dates[2])+Number(num));
var year = newDate.getYear()+1900;
var month = newDate.getMonth()+1;
var date = newDate.getDate();
if(Number(month)<10){
  month = "0"+month;
}
if(date<10){
  date = "0"+date;
}
return year+"-"+month+"-"+date;
}