This Gist shows an example where you can hard code starting address and ending address locations and the script will tell you the closest stations to your starting and ending trip points. Included as dependencies are jQuery and Google Maps API.

citibike-plotting-closest-station.html

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?libraries=places&amp;sensor=false"></script>
<script>

// Set starting addresses

var start_address = 'Union square NYC',
    end_address = 'Times Square NYC',
    start_station = '',
    end_station = '';

    console.log('start address: '+start_address);
    console.log('end address: '+end_address);

// Function to convert addresses to lat,lng

function getLatLng(start, end, callback) {
  var geocoder = new google.maps.Geocoder();

  // geocode the start
  geocoder.geocode({'address': start}, function(results, status) {  
    if (status == google.maps.GeocoderStatus.OK) {
      var startlat = results[0].geometry.location.lat();
      var startlng = results[0].geometry.location.lng();
      console.log('start latitude: '+startlat+', start longitude: '+startlng);

      // geocode the end
      geocoder.geocode({'address': end}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
          var endlat = results[0].geometry.location.lat();
          var endlng = results[0].geometry.location.lng();
          console.log('end latitude: '+endlat +', end longitude: '+endlng);
          //return [startlat, startlng, endlat, endlng];

          callback(startlat, startlng, endlat, endlng);
        }
      });
    }
  });
}

// Function to get distance between points

function getDistance(lat1,lng1,lat2,lng2) {
  //console.log('lat1: '+lat1+' is an: '+typeof lat1); // lat1: (40.759011, -73.98447220000003) is an: object 
  //console.log('lng1: '+lng1+' is an: '+typeof lng1); // lng1: undefined is an: undefined 
  //console.log('lat2: '+lat2+' is an: '+typeof lat2); // lat2: 40.76727216 is an: number 
  //console.log('lng2: '+lng2+' is an: '+typeof lng2); // lng2: -73.99392888 is an: number 
  var i = lat1.jb - lat2;
  var j = lat1.kb - lng2;
  //console.log(i);
  //console.log(j);
  var formula = i*i + j*j;
  return formula;
}

// Function to find the nearest station

function findNearestStation(lat,lng) {
  var min_distance = 99999,
      closest_station_id = 0;

  $.getJSON('stations.json', function(stations) {
    //console.log(stations);

    $.each(stations.stationBeanList, function(i, station) {

      var distance = getDistance(lat,lng, station.latitude, station.longitude); //call get distance
      //console.log(distance);
      if (distance < min_distance) {
        min_distance = distance;
        closest_station_id = i;
      }
    });
    console.log(closest_station_id);
    console.log(stations.stationBeanList[closest_station_id].stationName+' is the closest station.');
    return stations.stationBeanList[closest_station_id];
  });

}

// Call the getLatLng function to run and pass in callback function

getLatLng(start_address, end_address, function(start_lat, start_lng, end_lat, end_lng) {
  var start_p = new google.maps.LatLng(start_lat, start_lng),
      end_p = new google.maps.LatLng(end_lat, end_lng);
  start_station = findNearestStation(start_p); //call nearest station
  end_station = findNearestStation(end_p); //call nearest station
});
</script>