Ajax i http POST (php)

[ 2paca.zwaka @ 25.06.2011. 14:28 ] @

Imam neke podatke koje trebam da postujem na server gde se nalazi PHP skripta koja sve to prihvati i stavi u mySQL bazu......e sad problem nije php vec ajax(js) i http post........sto se tice php-a sve sam uradio al ovo me zeza.....

[ 2paca.zwaka @ 25.06.2011. 15:27 ] @

jsPost.html

Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
</head>
<script type="text/javascript">
function jsPost(){
        var http = new XMLHttpRequest();
        var url = "http://localhost/";
        var params = "a=nikola";
        http.open("POST", url, true);

        http.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        http.setRequestHeader("Content-length", params.length);

        http.send(params);
        http.onreadystatechange = function()
        {
            if(http.readyState == 4)
             {
                alert(http.responseText);
            }
        }

}
</script>
<body>
<button onclick="jsPost()" >Postuj</button>
</body>
</html>

index.pxp (u localhost folderu:sve to radi)

Code:

<?php
$a = $_POST["a"];
echo "Uspeh : ".$a;
?>

stvarno nemam pojma u cemu je greska