google_maps.js

<script type="text/javascript">
  var directionDisplay;
  var directionsService = new google.maps.DirectionsService();
  var map;

  function initialize() {
    directionsDisplay = new google.maps.DirectionsRenderer();
    var chicago = new google.maps.LatLng(37.7820, -122.4276);
    var mapOptions = {
      zoom:13,
      mapTypeId: google.maps.MapTypeId.ROADMAP,
      center: chicago
    }
    map = new google.maps.Map(document.getElementById('map_canvas'), mapOptions);
    directionsDisplay.setMap(map);
  }

  function calcRoute() {
    var start = "717 California St, San Francisco, CA 94108";
    var end = document.getElementById('address').innerHTML;
    var request = {
        origin:start,
        destination:end,
        travelMode: google.maps.DirectionsTravelMode.DRIVING
    };
    directionsService.route(request, function(response, status) {
      if (status == google.maps.DirectionsStatus.OK) {
        directionsDisplay.setDirections(response);
      }
    });
  }

  $(window).load(function(){
      initialize()
      calcRoute()
  });
</script>