Upload file to php

<span style="position: relative;">
    <button id="importGameButton">Importer spil</button>
    <input id="importGame" type="file" style="position: absolute; left: 0; top: 0; opacity: 0; cursor: pointer;" />
</span>

document.body.onload = function() {
var importGame = document.getElementById("importGame");
var importGameButton = document.getElementById("importGameButton");
importGame.style.width = importGameButton.clientWidth + "px";
importGame.style.height = importGameButton.clientHeight + "px";
}

importGame.onchange = function() {
                    var data = new FormData();
                    data.append("game", this.files[0]);
                    var sender = new XMLHttpRequest();
                    sender.open("post", "game.php", true);
                    sender.onreadystatechange = function() {
                        if (this.readyState == 4 && this.status == 200) {
                            loadGame(this.responseText);
                        }
                    }
                    sender.send(data);
                }