sendData:function(data , url) {
    var body = 'user='+JSON.stringify(data),
        request = new XMLHttpRequest(),
        url = url;
    request.open('POST', url, true);
    request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    request.setRequestHeader("X-Requested-With", "XMLHttpRequest");
    request.onreadystatechange = function() {
        if(this.readyState == 4) {
            if(this.status == 200) {
                if(this.responseText != null) {
                    document.getElementById('info').innerHTML =  request.responseText;
                }
                else{
                    alert('Ошибка Ajax: Данные не получены!');
                }
            }else{
                alert('Ошибка Ajax: '+ this.statusText);
            }
        }
    }
    request.send(body);
},

if(isset($_POST['user'])){

$data = json_decode($_POST['user'],true);
$decodedpass = md5(md5(trim($data['password'])));
$pass = substr($decodedpass, 0,13);
$query = $mysqli->query("SELECT user_login, user_password FROM users WHERE user_login = '". $mysqli->real_escape_string($data['login'])."'");
$queryArray = $query->fetch_assoc();

if($data['login'] === $queryArray['user_login'] && $pass === $queryArray['user_password']){

    $user_hash = generateCode(10);
    $mysqli->query("UPDATE users SET user_hash = '".$user_hash."' WHERE user_login='".$mysqli->real_escape_string($data['login'])."'");
    setcookie('user_hash', $user_hash, time() + 60*60*24*30);
    setcookie('user_name', $data['login'], time() + 60*60*24*30);
    header("Location: http://tasks/task_1/php/user_page.php"); # не работает
}else{
    echo 'Wrong data';
}