JS日期相加

 function addDate(type,NumDay,dtDate)

  {
     var date = new Date(dtDate)
     type = parseInt(type) //类型 
     var lIntval = parseInt(NumDay)//间隔
     switch(type){
         case 6 ://年
         date.setYear(date.getYear() + lIntval)
         break;
         case 7 ://季度
         date.setMonth(date.getMonth() + (lIntval * 3) )
         break;
         case 5 ://月
         date.setMonth(date.getMonth() + lIntval)
         break;
         case 4 ://天
         date.setDate(date.getDate() + lIntval)
         break
         case 3 ://时
         date.setHours(date.getHours() + lIntval)
         break
         case 2 ://分
         date.setMinutes(date.getMinutes() + lIntval)
         break
         case 1 ://秒
         date.setSeconds(date.getSeconds() + lIntval)
         break;
         default:
            
 }
         return date.getYear() +'-' +  (date.getMonth()+1) + '-' +date.getDate()+ ' '+    date.getHours()+':'+date.getMinutes()+':'+date.getSeconds()
  }

alert(addDate("4",1,"2009/5/31 00:00:00"))