在指定日期上添加年，月，日，时...等

                //取当前日期
                var date = new Date();
                var now = "";
                now = date.getFullYear()+"-"; //读英文就行了
                var mStr=new String(date.getMonth()+1);
                var dStr=new String(date.getDate());
                if (mStr.length==1){
                      mStr="0"+mStr;
                }
                if (dStr.length==1){
                      dStr="0"+dStr;
                }
                now = now + mStr +"-";
                now = now + dStr;              
                var test= DateAdd("d",1,now); 

function   DateAdd(strInterval,   NumDay,   dtDate)   {  

              var   dtTmp   =   new   Date(dtDate);  
              if   (isNaN(dtTmp))   dtTmp   =   new   Date();  
              switch   (strInterval)   {  
              case   "s":
                   dtTmp  =   new   Date(Date.parse(dtTmp)   +   (1000   *   NumDay));
                break;
              case   "n":
                   dtTmp  =   new   Date(Date.parse(dtTmp)   +   (60000   *   NumDay));
                break;
              case   "h":
                   dtTmp  =   new   Date(Date.parse(dtTmp)   +   (3600000   *   NumDay));
                break;
              case   "d":
                   dtTmp  =   new   Date(Date.parse(dtTmp)   +   (86400000   *   NumDay));
                break;
              case   "w":
                   dtTmp  =   new   Date(Date.parse(dtTmp)   +   ((86400000   *   7)   *   NumDay));
                break;
              case   "m":
                   dtTmp  =   new   Date(dtTmp.getFullYear(),   (dtTmp.getMonth())   +   NumDay,   dtTmp.getDate(),   dtTmp.getHours(),   dtTmp.getMinutes(),   dtTmp.getSeconds());
                break;  
              case   "y":
                   dtTmp  =   new   Date((dtTmp.getFullYear()   +   NumDay),   dtTmp.getMonth(),   dtTmp.getDate(),   dtTmp.getHours(),   dtTmp.getMinutes(),   dtTmp.getSeconds());
                break;
              }
              var mStr=new String(dtTmp.getMonth()+1);
              var dStr=new String(dtTmp.getDate());
              if (mStr.length==1){
                  mStr="0"+mStr;
              }
              if (dStr.length==1){
                  dStr="0"+dStr;
              }
              return dtTmp.getFullYear()+"-"+mStr+"-"+dStr;
  }