Login system with MooTools (Ajax)
//Connect, prepare, execute and bind
$mysqli = new mysqli('localhost','root','','db');
$stmt = $mysqli->prepare("SELECT id, username, password FROM users WHERE username=?");
$stmt->bind_param('s',//I need to get the typed in username from the index.php file);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($get_id, $get_username, $get_password);
$stmt->fetch();

if($stmt->num_rows!=0){
    //Check if the passwords match
    if($get_password==//I need the typed in password here){
        echo('Passwords match');
    }
}
else{
        echo 'User dosn't exist';
}

// JavaScript (MooTools):
var myRequest = new Request([method:"POST", url:"login-process.php", onSuccess:  function(responseText){
    document.id('response').set('text', responseText);
}]);
myRequest.send("username="+username+"&password="+password);