Google Map - MGRS, Lat, Lon, and dragable marker

HTML

<script src="http://maps.google.com/maps/api/js?sensor=false&amp;.js"></script>
<script src="https://maps.google.com/maps/api/js?sensor=false&amp;.js"></script>
<div id="map"></div>
<label for="lat">Lattitude:</label>
<input id="lat" value="12" />
<label for="lat">Longitude:</label>
<input id="lon" value="12.03" />
<br/>
<label for="mgrs">MGRS:</label>
<input id="mgrs" value="34PDV552" />

CSS

#map {
  width: 450px;
  height: 400px;
}

JavaScript

var map;
var marker;

function initialize() {
  var lattitude = $('#lat');
  var longitude = $('#lon');
  var mgrs = $('#mgrs');

  if (lattitude.val() && longitude.val()) {
    if (!mgrs.val()) {
      mgrs.val(getMGRSFromLatLon(lattitude.val(), longitude.val()));
    }
  } else if (mgrs.val()) {
    setLatLonFromMGRS(mgrs.val());
    centerMapOnLatLon();
  }

  var mapOptions = {
    zoom: 5,
    center: new google.maps.LatLng(lattitude.val(), longitude.val()),
    mapTypeId: google.maps.MapTypeId.ROADMAP
  };

  map = new google.maps.Map(document.getElementById('map'), mapOptions);

  marker = new google.maps.Marker({
    position: new google.maps.LatLng(lattitude.val(), longitude.val()),
    map: map,
    draggable: true,
    animation: google.maps.Animation.DROP
  });

  google.maps.event.addListener(marker, "dragend", function(event) {
    var lat = event.latLng.lat();
    var lng = event.latLng.lng();
    $('#lat').val(lat);
    $('#lon').val(lng);
    $('#mgrs').val(getMGRSFromLatLon(lat, lng));
  });
}

google.maps.event.addDomListener(window, 'load', initialize);

$('#mgrs').change(function() {
  setLatLonFromMGRS($(this).val());
  centerMapOnLatLon();
});

var setLatLonFromMGRS = function(mgrs) {
  var latLon = getLatLonFromMGRS(mgrs);
  var lat = latLon[0];
  var lon = latLon[1];
  $('#lat').val(lat);
  $('#lon').val(lon);
}

$('#lat, #lon').change(function() {
  updateLatLon();
});

var updateLatLon = function() {
  var lat = $('#lat').val();
  var lon = $('#lon').val();
  if (lat && lon) {
    var mgrs = getMGRSFromLatLon(lat, lon);
    $('#mgrs').val(mgrs);
    centerMapOnLatLon();
  }
};

var centerMapOnLatLon = function() {
  var lat = $('#lat').val();
  var lon = $('#lon').val();
  var latlng = new google.maps.LatLng(lat, lon);
  marker.setPosition(latlng);
  map.setCenter(marker.getPosition());
};

var getMGRSFromLatLon = function(lat, lon) {
  return usng.LLtoUSNG(lat, lon, 5).split(' ').join('');
};

var getLatLonFromMGRS = function(mgrs) {
 ...