function isEmail(str) {
  return ((str != "") && (str.indexOf("@") != -1) && (str.indexOf(".") != -1));}

function validateForm(form) {
    if(document.feedback.mail_subject.value.length < 1) {
        alert("請填寫主題");
                document.feedback.mail_subject.focus();
        return false;
      }
    if(document.feedback.message.value.length < 1) {
        alert("請填寫問題或意見");
                document.feedback.message.focus();
        return false;
      }
    if(document.feedback.name.value.length < 1) {
        alert("請填寫你的姓名");
                document.feedback.name.focus();
        return false;
      }
    if( !isEmail(document.feedback.email.value) ){
        alert("請提供正確的電郵地址");
                document.feedback.email.focus();
        return false;
      }
    if( !isEmail(document.feedback.emailconfirm.value) ){
        alert("請再次輸入電郵地址");
                document.feedback.emailconfirm.focus();
        return false;
      }
    if ( document.feedback.emailconfirm.value != document.feedback.email.value){
        alert("你輸入的電郵地址並不相符");
                document.feedback.email.focus();
        return false;
      }
      }�