通过原生js操作input值

function subCardNmbr(){
       var cardNmbr = document.getElementById("cardNmbr").value;
       if(cardNmbr=="" && cardNmbr == undefined){
              alert("请输入卡号");
              return false;
       }
       document.getElementById("cardNmbr").value="";
              frm.submit();
       }
}