This example uses a data layer to dynamically change the appearance of some
[Data.Feature](https://developers.google.com/maps/documentation/javascript/reference/data.md.txt#Data.Feature)
objects when the user hovers over or clicks them.

Read the
[documentation](https://developers.google.com/maps/documentation/javascript/datalayer.md.txt#change_appearance_dynamically).
<iframe src="https://geo-devrel-javascript-samples.web.app/samples/layer-data-dynamic/app/dist/" allow="fullscreen; "></iframe>

### TypeScript

```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") as string;
    }
    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;
```

> [!NOTE]
> **Note:** Read the [guide](https://developers.google.com/maps/documentation/javascript/using-typescript.md.txt) on using TypeScript and Google Maps.

### JavaScript

```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;
```

> [!NOTE]
> **Note:** The JavaScript is compiled from the TypeScript snippet.

### CSS

```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
<html>
  <head>
    <title>Data Layer: Dynamic Styling</title>

    <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 script 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. See
      https://developers.google.com/maps/documentation/javascript/load-maps-js-api
      for more information.
      -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&v=weekly"
      defer
    ></script>
  </body>
</html>
```

### Clone Sample


Git and Node.js are required to run this sample locally. Follow these [instructions](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) to install Node.js and NPM. The following commands clone, install dependencies and start the sample application.

```javascript
  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`.

```javascript
  git checkout sample-SAMPLE_NAME
  npm i
  npm start
```