javascript detect arrow key press

1//detecting arrow key presses
2document.addEventListener('keydown', function(e) {
3    switch (e.keyCode) {
4        case 37:
5            alert('left');
6            break;
7        case 38:
8           alert('up');
9            break;
10        case 39:
11            alert('right');
12            break;
13        case 40:
14            alert('down');
15            break;
16    }
17});