js禁掉回车键form提交

<script language="javascript" type="text/javascript">     document.onkeydown = function (event) {         var target, code, tag;         if (!event) {             event = window.event; //针对ie浏览器              target = event.srcElement;             code = event.keyCode;             if (code == 13) {                 tag = target.tagName;                 if (tag == "TEXTAREA") { return true; }                 else { return false; }             }         }         else {             target = event.target; //针对遵循w3c标准的浏览器，如Firefox              code = event.keyCode;             if (code == 13) {                 tag = target.tagName;                 if (tag == "INPUT") { return false; }                 else { return true; }             }         }     }; </script>