Question

here is the code for adding to database:

<?php 
/*Config*/

Answer 1

Sounds like something that should be able to be easily accomplished using a PHP session variable.

Just use sessions and set a session variable (call it posted or something) and if that variable is set, don’t allow the user to post (hide the submit button or use a PHP if-statement in your javascript to only perform the action when that variable is not set).

The session will be cleared when the user closes the browser.

As a possible example, in your PHP code for adding to the database, just put this at the beginning:

session_start();
if (isset($_SESSION['posted']))
    die("posted");
$_SESSION['posted'] = true;

---

EDIT :

You just need to add another else if statement. It will look something like this:

if(response == "knownudid"){
    document.getElementById('udid_message').innerHTML = '<br><i><font color="red">This UDID has already been inserted and it is valid.</font></i>' ;
}else if(response == "noudid"){
    document.getElementById('udid_message').innerHTML = '<br><i><font color="orange">Please, enter your UDID.</font></i>' ;
}else if(response == "errudid"){
    document.getElementById('udid_message').innerHTML = '<br><i><font color="red">It seems this UDID is not correct. Please check for typo.</font></i>' ;
}else if(response == "validatedudid"){
    document.getElementById('udid_message').innerHTML = '<br><i><font color="green">This UDID has been found as an invalid one. Now it is valid.</font></i>' ;
}else if(response == "posted"){    // Here is the new one
    document.getElementById('udid_message').innerHTML = '<br><i><font color="red">You have already posted a UDID for this session.</font></i>' ;
}else{
    document.getElementById('udid_message').innerHTML = '<br><i><font color="green">UDID <b>'+response+'</b> successfully inserted.</font></i>';
}