var asubmit = document.getElementById("submit");

<span style="white-space:pre"> </span>asubmit.setAttribute("onclick","alert('請檢查手機號碼');"); //在火狐中有效，而在ie中無效

<span style="white-space:pre"> asubmit.setAttribute("onclick","javascript:document.buyform.submit();");</span> //在ie中有效，火狐也有效