gmaps.html

<!DOCTYPE html>
<html>
  <head>
    <style>
      /* Always set the map height explicitly to define the size of the div
       * element that contains the map. */
      #map {
        height: 100%;
      }
      /* Optional: Makes the sample page fill the window. */
      html, body {
        height: 100%;
        margin: 0;
        padding: 0;
      }
    </style>
  </head>
  <body>
    <div id="map"></div>
    <script>
      var map;
      function initMap() {
        map = new google.maps.Map(document.getElementById('map'), {
          zoom: 2,
          center: new google.maps.LatLng(2.8,-187.3),
          mapTypeId: 'terrain'
        });
        // NOTE: This uses cross-domain XHR, and may not work on older browsers.
    var geojson =  map.data.loadGeoJson(
          'geoJSON/battleOfTheBulge.json');
      }

      var markerCollection = map.data.addGeoJson(geoJson);
  for (var i = 0, length = markerCollection.length; i < length; i++) {
    var feature = markerCollection[i];
    debugger;
    if (feature.getProperty('icon')) {
      map.data.setStyle(function(feature) {
        return {
          icon: feature.getProperty('icon')
        };
      });
    }
  }

      // create a timeslider: https://code.google.com/archive/p/timemap/
      // https://stackoverflow.com/questions/26683375/loading-json-into-timemap


      //   // Create a <script> tag and set the USGS URL as the source.
      //   var script = document.createElement('script');
      //   // This example uses a local copy of the GeoJSON stored at
      //   // http://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/2.5_week.geojsonp
      //   script.src = 'https://developers.google.com/maps/documentation/javascript/examples/json/earthquake_GeoJSONP.js';
      //   document.getElementsByTagName('head')[0].appendChild(script);
      // }

      // Loop through the results array and place a marker for each
      // set of coordinates.

    </script>
    <script async defer
    src="https://maps.googleapis.com/maps/api/js?key=AIzaSyDKkFd761EWHZySFBmGiSaksxwn4zDPIYI&callback=initMap">
    </script>
  </body>
</html>