var directionDisplay;
var directionsService = new google.maps.DirectionsService();
var map;

function initialize() {
  directionsDisplay = new google.maps.DirectionsRenderer();
  var latlng = new google.maps.LatLng(34.141254, -118.079902);
  var myOptions = {
    zoom:15,
    mapTypeId: google.maps.MapTypeId.ROADMAP,
    center: latlng
  }
  map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
  directionsDisplay.setMap(map);
  directionsDisplay.setPanel(document.getElementById("directionsPanel"));

var marker = new google.maps.Marker({
      position: latlng, 
      map: map, 
      title:"This is the location"
  });

}
  
function calcRoute() {
  var start = document.getElementById("start").value;
  var end = document.getElementById("end").value;
  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);
    }
  });
}