Why does my AJAX validation code not work properly?

Question

I made a website that depends on PHP, AJAX and Javascript.
The problem here is that the website is unstable which means sometimes the validation is working and some times it is not working at all.
The validation code is written in JavaScript. Does this mean that we need more special conditions?

The code for validation:

<script language=Javascript>
function Inint_AJAX() {
try { return new ActiveXObject("Msxml2.XMLHTTP");  } catch(e) {} //IE
try { return new ActiveXObject("Microsoft.XMLHTTP"); } catch(e) {} //IE
try { return new XMLHttpRequest();  } catch(e) {} //Native Javascript
alert("XMLHttpRequest not supported");
return null;
};

function dochange(src, val) 
{
 var req = Inint_AJAX();
 req.onreadystatechange = function () 
 {
      if (req.readyState==4) 
      {
           if (req.status==200) 
        { 
                document.getElementById(src).innerHTML=req.responseText;
           }
      }
 };
 req.open("GET", "traditional_locate.php?data="+src+"&val="+val);
  req.send(null);
}

window.onLoad=dochange('cities', -1); 


function submitform()
{
 if(document.form1.onsubmit())
 {
    document.form1.submit();
 }
}

function validate()
{
  var p_o_box=(document.form1.p_o_box.value);
  var owner_name=(document.form1.owner_name.value);
  var cities=(document.form1.cities.value);
  var post_office=(document.form1.post_office.value);   


     if(cities == 0)
     {
      alert("Please Choose city");
      document.form1.cities.focus();
      return false;
     }

     else if(post_office == 0)
      {
      alert("Please Choose post office");
      document.form1.post_office.focus();

      return false;
      }

      else if (p_o_box=="")
       {
        alert ("Please Write P.O.Box");
        document.form1.p_o_box.focus();
         return false;      
       } 

       else if(owner_name=="")
         {
         alert("Please Write Owner Name");
         return false;
         }

        else if(p_o_box!="")
            {
                 var a=new Array;

           <?php
           session_start();         
           $zipinfo=$_SESSION[zip_code];         
           $conn=mysql_connect('localhost','root','');
           mysql_select_db('post_db',$conn);
           $query="select p_o_box from p_o_box where zip_code='$zipinfo' ";
           $result = mysql_query ($query , $conn ) or die ( mysql_error ());
           $rows=mysql_num_rows($result);
           $n = array();
           for($i=0;$i<$rows;$i++)
           {
            $data=mysql_fetch_row($result);
            $n[] = $data[0]; 
           }

           for($i=0;$i<count($n); $i++)
           {
            echo "a[$i]='".$n[$i]."';\n";
           }   
           ?>

           var ss=0;
           for(i=0;i<a.length;i++)

           if(a[i]==p_o_box)
            {
             var ss=1;
            }

            if (ss==0)
               {
             alert('not correct p.o. box');
             document.form1.p_o_box.focus();
               return false;
              }
           else
               { return true;}

         }      


    return true;  
}

</script>

Answer 1

Validation should be done on the server side. What happens when a use disables their JavaScript?

Also, that block of JavaScript will only execute the PHP when the page loads, and not everytime the user validates.

Answer 2

Very hard to answer because I don't see a question. What exactly does not work?

But I can suppose some problems:

• Are you sure, that body.onload runs? Sometimes doesn't...
• scripting is not crossbrowser
• session_start() should fail because there is an output before and headers can't be sent.
• you said that validation fails, but where is it being called?

please, provide more exact question and more clear example of code which does not work (i.e. I'm not sure, that source of submitform() is so nessecary).