d3 zoom and pan from the keyboard

zoompan.js

d3.select('body').on('keydown', function () {
    var step = 200;
    var key = d3.event.key || d3.event.keyCode; // safari doesn't know .key
    switch (key) {
    case 'Esc':
    case 27:
        zoom.translate([0, 0]).scale(1).event(mapsvg.transition());
        break;
    case '+':
    case '=':
    case 187:
        zoomByFactor(2);
        break;
    case '-':
    case 189:
        zoomByFactor(1 / 2);
        break;
    case 'Left':
    case 37:
        zoom.translate([zoom.translate()[0] + step, zoom.translate()[1]]).event(mapsvg.transition());
        break;
    case 'Right':
    case 39:
        zoom.translate([zoom.translate()[0] - step, zoom.translate()[1]]).event(mapsvg.transition());
        break;
    case 'Up':
    case 38:
        zoom.translate([zoom.translate()[0], zoom.translate()[1] + step]).event(mapsvg.transition());
        break;
    case 'Down':
    case 40:
        zoom.translate([zoom.translate()[0], zoom.translate()[1] - step]).event(mapsvg.transition());
        break;
    default:
        debug('key pressed: \'' + key + '\'');

    }
});