function isblank(s)
  {
      for(var i = 0; i < s.length; i++) {
          var c = s.charAt(i);
          if ((c != ' ') && (c != '\n') && (c != '\t')) return false;
      }
      return true;
  }
  
  function Validate_Form(f)
  {
      var msg="";
      var empty_fields = "";
      var errors = "";

      msg += "Form Incomplete\n";
      msg += "__________________\n\n"
  
      if (isblank(f.realname.value)) {
        msg += " · Your name is required\n";
        errors = "Y";
      }
      if (isblank(f.postcode.value)) {
        msg += " · Your postcode is required\n";
        errors = "Y";
      }
      if (isblank(f.email.value)) {
        msg += " · Your email address is required\n";
        errors = "Y";
      }
      if (isblank(f.tel.value)) {
        msg += " · Your telephone number is required\n";
        errors = "Y";
      }
  
      if (!errors) return true;
  
      alert(msg);
  
      return false;
  }