Add Marker function with Google Maps API

I have the following Javascript that includes both the standard Google Maps API initialize() function and custom addMarker() function. The map will load fine however the marker does not get added to the map.

<script type="text/javascript">

    // Standard google maps function
    function initialize() {
        var myLatlng = new google.maps.LatLng(40.779502, -73.967857);
        var myOptions = {
            zoom: 12,
            center: myLatlng,
            mapTypeId: google.maps.MapTypeId.ROADMAP
        }
        map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
    }

    // Function for adding a marker to the page开发者_如何学运维.
    function addMarker(location) {
        marker = new google.maps.Marker({
            position: location,
            map: map
        });
    }

    // Testing the addMarker function
    CentralPark = new google.maps.LatLng(37.7699298, -122.4469157);
    addMarker(CentralPark);

</script>

You have added the add marker method call outside the function and that causes it to execute before the initialize method which will be called when google maps script loads and thus the marker is not added because map is not initialized Do as below.... Create separate method TestMarker and call it from initialize.

<script type="text/javascript">

    // Standard google maps function
    function initialize() {
        var myLatlng = new google.maps.LatLng(40.779502, -73.967857);
        var myOptions = {
            zoom: 12,
            center: myLatlng,
            mapTypeId: google.maps.MapTypeId.ROADMAP
        }
        map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
        TestMarker();
    }

    // Function for adding a marker to the page.
    function addMarker(location) {
        marker = new google.maps.Marker({
            position: location,
            map: map
        });
    }

    // Testing the addMarker function
    function TestMarker() {
           CentralPark = new google.maps.LatLng(37.7699298, -122.4469157);
           addMarker(CentralPark);
    }
</script>

function initialize() {
    var location = new google.maps.LatLng(44.5403, -78.5463);
    var mapCanvas = document.getElementById('map_canvas');
    var map_options = {
      center: location,
      zoom: 15,
      mapTypeId: google.maps.MapTypeId.ROADMAP
    }
    var map = new google.maps.Map(map_canvas, map_options);

    new google.maps.Marker({
        position: location,
        map: map
    });
}
google.maps.event.addDomListener(window, 'load', initialize);

THis is other method
You can also use setCenter method with add new marker

check below code

$('#my_map').gmap3({
      action: 'setCenter',
      map:{
         options:{
          zoom: 10
         }
      },
      marker:{
         values:
          [
            {latLng:[position.coords.latitude, position.coords.longitude], data:"Netherlands !"}
          ]
      }
   });

<div id="map" style="width:100%;height:500px"></div>

<script>
function myMap() {
  var myCenter = new google.maps.LatLng(51.508742,-0.120850);
  var mapCanvas = document.getElementById("map");
  var mapOptions = {center: myCenter, zoom: 5};
  var map = new google.maps.Map(mapCanvas, mapOptions);
  var marker = new google.maps.Marker({position:myCenter});
  marker.setMap(map);
}
</script>

<script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyBu-916DdpKAjTmJNIgngS6HL_kDIKU0aU&callback=myMap"></script>

Below code works for me:

<script src="http://maps.googleapis.com/maps/api/js"></script>
<script>
    var myCenter = new google.maps.LatLng(51.528308, -0.3817765);

    function initialize() {
           var mapProp = {
            center:myCenter,
            zoom:15,
            mapTypeId:google.maps.MapTypeId.ROADMAP
        };
        var map = new google.maps.Map(document.getElementById("googleMap"), mapProp); 

        var marker = new google.maps.Marker({
            position: myCenter,
            icon: {
                url: '/images/marker.png',
                size: new google.maps.Size(70, 86), //marker image size
                origin: new google.maps.Point(0, 0), // marker origin
                anchor: new google.maps.Point(35, 86) // X-axis value (35, half of marker width) and 86 is Y-axis value (height of the marker).
            }
        });

        marker.setMap(map);

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

</script>
<body>
<div id="googleMap" style="width:500px;height:380px;"></div>
</body>

Reference link