document.onkeydown = function(e) {
if (e.keyCode == 37) {
posX = document.querySelector('.player').offsetLeft;
xn = posX - 50;
var timerId = setTimeout(function() {
document.querySelector('.player').style.left = xn + 'px';
}, 0);
}
}
document.onkeyup = function(e) {
if (e.keyCode == 37) {
clearTimeout(timerId);
}
}