dist/samples/layer-data-dynamic/inline.html

<!DOCTYPE html>
<html>
  <head>
    <title>Data Layer: Dynamic Styling</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>
    <script
      src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap&libraries=&v=weekly"
      defer
    ></script>
    <style type="text/css">
      /* 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>
    <script>
      let map;

      function initMap() {
        map = new google.maps.Map(document.getElementById("map"), {
          zoom: 4,
          center: { lat: -28, lng: 137 },
        });
        // Load GeoJSON.
        map.data.loadGeoJson(
          "https://storage.googleapis.com/mapsdevsite/json/google.json"
        );
        // Color each letter gray. Change the color when the isColorful property
        // is set to true.
        map.data.setStyle((feature) => {
          let color = "gray";

          if (feature.getProperty("isColorful")) {
            color = feature.getProperty("color");
          }
          return /** @type {!google.maps.Data.StyleOptions} */ {
            fillColor: color,
            strokeColor: color,
            strokeWeight: 2,
          };
        });
        // When the user clicks, set 'isColorful', changing the color of the letters.
        map.data.addListener("click", (event) => {
          event.feature.setProperty("isColorful", true);
        });
        // When the user hovers, tempt them to click by outlining the letters.
        // Call revertStyle() to remove all overrides. This will use the style rules
        // defined in the function passed to setStyle()
        map.data.addListener("mouseover", (event) => {
          map.data.revertStyle();
          map.data.overrideStyle(event.feature, { strokeWeight: 8 });
        });
        map.data.addListener("mouseout", (event) => {
          map.data.revertStyle();
        });
      }
    </script>
  </head>
  <body>
    <div id="map"></div>
  </body>
</html>