function mycheck(){
var loginSelect = myform.loginSelect.value;
if(myform.username.value=="")
{alert("用户名称不能为空！！");myform.username.focus();return false;}
if(myform.password.value=="")
{alert("用户密码不能为空！！");myform.password.focus();return false;}
document.myform.action = document.forms[0].loginSelect.value;
myform.submit();
}