来自表单字段的Javascript电子邮件验证突然不起作用？

Question

在曾经有过工作电子邮件验证的网页上工作，但在添加一些其他功能后，它突然不再有效。页面不应该继续，除非所有字段都有效，如果你想知道为什么它有点像一个奇怪的网站，一切基本上都是客户端。

最初，如果字段为空白或没有“@”和“。”，则电子邮件验证有效。在它之后，使用代码：

  if (d==null || d=="")
  {
  document.forms["registration"]["email"].focus();
  alert("Please enter your email address");
  return false;
}
else
    {
        var emailAddress = d;
        var atLoc = emailAddress.indexOf("@",1);
        var dotLoc = emailAddress.indexOf(".",atLoc+2);
        var len = emailAddress.length;

        if (atLoc > 0 && dotLoc > 0 && len > dotLoc+2)
        {
            return true;
        }
        else
        {
            alert("Invalid E-mail address format! Please enter your e-mail address again.");
            document.forms["registration"]["email"].focus();
            return false;
        }
    }

然而，添加了整个代码：

    function validateForm(){

{
  var f=document.forms["registration"]["FirstName"].value;
  var a=document.forms["registration"]["Surname"].value;
  var b=document.forms["registration"]["address"].value;
  var c=document.forms["registration"]["post"].value;
  var d=document.forms["registration"]["email"].value;
  var z=document.forms["registration"]["password"].value;

  if (f==null || f=="")
  {
  document.forms["registration"]["FirstName"].focus();
  alert("Please enter your first name");

  return false;
}
if (a==null || a=="")
  {
  document.forms["registration"]["Surname"].focus();
  alert("Please enter your surname");
  return false;
}


if (b==null || b=="")
  {
  alert("Please enter your address");
  document.forms["registration"]["address"].focus();
  return false;
}
if (c==null || c=="")
  {
  alert("Please enter your postcode");
  document.forms["registration"]["post"].focus();
  return false;
}
if (d==null || d=="")
  {
  document.forms["registration"]["email"].focus();
  alert("Please enter your email address");
  return false;
}
else
    {
        var emailAddress = d;
        var atLoc = emailAddress.indexOf("@",1);
        var dotLoc = emailAddress.indexOf(".",atLoc+2);
        var len = emailAddress.length;

        if (atLoc > 0 && dotLoc > 0 && len > dotLoc+2)
        {
            return true;
        }
        else
        {
            alert("Invalid E-mail address format! Please enter your e-mail address again.");
            document.forms["registration"]["email"].focus();
            return false;
        }
    }

}
}

它不再有效......？困惑，任何帮助表示赞赏。