php - Ajax check if username exists

I am having trouble to get my code working. As a user types in a username it checks the database to see if it exists and if it does sets the <P id="checkusername"> to "Username Taken." and if not sets it to "Not Taken." I can't see why my code is not working.

1-register.html

<html>
  <body>
    <CENTER>
      <form name="register" action="register.php" method="post">
        Username: <input type="text" name="username" onkeyup="checkUsername(this.value)" />
        <P id="checkusername">checker</P> 
        <input type="submit" value="Login" />      
      </form>
    </CENTER>

    <script type="text/javascript">
      function checkUsername(){
        var xmlhttp;
        var username=document.forms["register"]["username"].value;
        if(username.length==0){
          document.getElementById("checkusername").innerHTML="Empty";
          return;
        }
        if(window.XMLHttpRequest){
          xmlhttp=new XMLHttpRequest();
        }else{
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }

        var url = "login.php";
        var params = "header=checkusername&username="+username+"&password="";
        xmlhttp.open("POST", url, true);
        xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        xmlhttp.setRequestHeader("Content-length", params.length);
        xmlhttp.setRequestHeader("Connection", "close");

        xmlhttp.onreadystatechange = function() {//Call a function when the state changes.
    if(xmlhttp.readyState == 4 && xmlhttp.status == 200){
          document.getElementById("checkusername").innerHTML=xmlhttp.responseText;
    }
      }
      xmlhttp.send(params);
    }
    </script>
  </body>
</html>

2-register.php

<?php
  $header = $_POST["header"];
  if(header=="checkusername"){
    checkusername($_POST["username"]);
  }else{
    echo "No match: " . $header;
  }

  function connection(){
    $con = mysql_connect(URL, username, password);
    if(!$con){
      die('Could not connect: ' . mysql_error());
    }
    return $con;
  }
  function checkusername($username){
    $con = connection();
    mysql_select_db(database, $con);
    $result = mysql_query("SELECT * FROM users WHERE username = \"" . $username . "\";");
    while($row = mysql_fetch_array($result)){
      if(($row['username'] == $username)){
        echo "Username Taken.<br/>";
        return;
      }
    }
    echo "Not Taken.";
  }
  mysql_close();
?>

1-register.html

<html>
  <body>
    <CENTER>
      <form name="register" action="register.php" method="post">
        Username: <input type="text" name="username" onkeyup="checkUsername(this.value)" />
        <P id="checkusername">checker</P> 
        <input type="submit" value="Login" />      
      </form>
    </CENTER>

    <script type="text/javascript">
      function checkUsername(){
        var xmlhttp;
        var username=document.forms["register"]["username"].value;
        if(username.length==0){
          document.getElementById("checkusername").innerHTML="Empty";
          return;
        }
        if(window.XMLHttpRequest){
          xmlhttp=new XMLHttpRequest();
        }else{
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }

        var url = "login.php";
        var params = "header=checkusername&username="+username+"&password="";
        xmlhttp.open("POST", url, true);
        xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        xmlhttp.setRequestHeader("Content-length", params.length);
        xmlhttp.setRequestHeader("Connection", "close");

        xmlhttp.onreadystatechange = function() {//Call a function when the state changes.
    if(xmlhttp.readyState == 4 && xmlhttp.status == 200){
          document.getElementById("checkusername").innerHTML=xmlhttp.responseText;
    }
      }
      xmlhttp.send(params);
    }
    </script>
  </body>
</html>

2-register.php

<?php
  $header = $_POST["header"];
  if(header=="checkusername"){
    checkusername($_POST["username"]);
  }else{
    echo "No match: " . $header;
  }

  function connection(){
    $con = mysql_connect(URL, username, password);
    if(!$con){
      die('Could not connect: ' . mysql_error());
    }
    return $con;
  }
  function checkusername($username){
    $con = connection();
    mysql_select_db(database, $con);
    $result = mysql_query("SELECT * FROM users WHERE username = \"" . $username . "\";");
    while($row = mysql_fetch_array($result)){
      if(($row['username'] == $username)){
        echo "Username Taken.<br/>";
        return;
      }
    }
    echo "Not Taken.";
  }
  mysql_close();
?>

Share Improve this question edited May 7, 2012 at 12:20 jprofitt 11k4 gold badges38 silver badges46 bronze badges asked May 7, 2012 at 12:18 sbnarra 5844 gold badges9 silver badges27 bronze badges

1 restrict your question to smaller code examples. And only the relevant parts. – Itay Moav -Malimovka Commented May 7, 2012 at 12:20
in your while loop in php file, you are always outputting "Not taken", it should be under with IF condition.. plus.. why you need to loop to see if username matches.. your sql already did that.. just see if count is 0 its not taken.else its taken – Kamal Commented May 7, 2012 at 12:21
1 @pom - if you are not willing to expand on that it doesn't really help anyone... – Lix Commented May 7, 2012 at 12:28
Don't use <center> it's deprecated! – skywalker Commented Dec 23, 2015 at 9:56

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