js监听键盘事件

如题

document.onkeydown = function(e) {
        switch((window.event||e).keyCode) {
            case 37:    Snake.direction = 2; break;     // ←
            case 38:    Snake.direction = 0; break;     // ↑
            case 39:    Snake.direction = 3; break;     // →
            case 40:    Snake.direction = 1;  break;     // ↓
            case 32:    Snake.startOrStop();
        }
};