JS判断文本框起始日期和结束日期间隔

<script type="text/javascript">
   function checkSelect()
   {
    var result = true;
    var errorMessage = "";
     
    if(document.getElementById('handle_workorder_report_form:queryDateF').value == "")
    {
     errorMessage += "起始日期 不能为空/n"
    }
    if(document.getElementById('handle_workorder_report_form:queryDateT').value == "")
    {
     errorMessage += "结束日期 不能为空/n"
    }
    else if(document.getElementById('handle_workorder_report_form:queryDateF').value != "")
    {
     var theSelectF = new  Date(document.getElementById('handle_workorder_report_form:queryDateF').value.replace(//-/g, "//"));
          
              var dSelectF = new  Date(document.getElementById('handle_workorder_report_form:queryDateF').value.replace(//-/g, "//"));
              var dSelectT = new  Date(document.getElementById('handle_workorder_report_form:queryDateT').value.replace(//-/g, "//"));
     
              var theFromM=dSelectF.getMonth();
              var theFromD=dSelectF.getDate();
              theFromM += 1;
              dSelectF.setMonth(theFromM, theFromD);
              if(theSelectF > dSelectT || dSelectF < dSelectT)
              {
                  errorMessage += "每次只能查询1个月范围内的数据/n";
              }
    }
    
    if(errorMessage.length > 0)
    {
     alert(errorMessage);
     result = false;
    }
    return result;
   }
  </script>