Data Layer: Dynamic Styling

This example uses a data layer to dynamically change the appearance of some KML feature objects when the user hovers over or clicks them.

Read the documentation.

TypeScript

let map: google.maps.Map;

function initMap(): void {
  map = new google.maps.Map(document.getElementById("map") as HTMLElement, {
    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();
  });
}

declare global {
  interface Window {
    initMap: () => void;
  }
}
window.initMap = initMap;

JavaScript

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();
  });
}

window.initMap = initMap;

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;
}

HTML

<html>
  <head>
    <title>Data Layer: Dynamic Styling</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>

    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script type="module" src="./index.js"></script>
  </head>
  <body>
    <div id="map"></div>

    <!-- 
     The `defer` attribute causes the callback to execute after the full HTML
     document has been parsed. For non-blocking uses, avoiding race conditions,
     and consistent behavior across browsers, consider loading using Promises
     with https://www.npmjs.com/package/@googlemaps/js-api-loader.
    -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&v=weekly"
      defer
    ></script>
  </body>
</html>

Try Sample

Clone Sample

Git and Node.js are required to run this sample locally. Follow these instructions to install Node.js and NPM. The following commands clone, install dependencies and start the sample application.

  git clone -b sample-layer-data-dynamic https://github.com/googlemaps/js-samples.git
  cd js-samples
  npm i
  npm start

Other samples can be tried by switching to any branch beginning with sample-SAMPLE_NAME.

  git checkout sample-SAMPLE_NAME
  npm i
  npm start