function chkEmpty(obj,alarm){
	if($.trim(obj.val()).length < 1){
		obj.focus();
		alert(alarm);
		return true;
	}

	return false;
}
$(document).ready(function(){
	$('#membership').submit(function(){
		if(chkEmpty($('#username'),'Please enter your ID.')) return false;
		if(chkEmpty($('#password'),'Please enter your password.')) return false;
		return true;
	});
})