Data Layer: Event Handling

  • This example demonstrates dynamically displaying information from a data layer when the mouse hovers over a KML feature object on a Google Map.

  • It uses GeoJSON data loaded onto the map and styled with custom colors and stroke weights.

  • A mouseover event listener is added to each feature, triggering the display of a specific property ("letter") in an info box.

  • The sample includes code in TypeScript and JavaScript, along with HTML and CSS for styling and structure.

This example uses a data layer to dynamically display information about a KML feature object when under the mouse cursor.

Read the documentation.

TypeScript

async function init() {
    await google.maps.importLibrary('maps');

    const mapElement = document.querySelector('gmp-map')!;

    const innerMap = mapElement.innerMap;

    // Load GeoJSON.
    innerMap.data.loadGeoJson('google.json');

    // Add some style.
    innerMap.data.setStyle((feature) => {
        return {
            fillColor: feature.getProperty('color') as string,
            strokeWeight: 1,
        };
    });

    // Set mouseover event for each feature.
    innerMap.data.addListener(
        'mouseover',
        (event: google.maps.Data.MouseEvent) => {
            document.getElementById('info-box')!.textContent =
                event.feature.getProperty('letter') as string;
        }
    );
}

void init();

JavaScript

async function init() {
    await google.maps.importLibrary('maps');

    const mapElement = document.querySelector('gmp-map');

    const innerMap = mapElement.innerMap;

    // Load GeoJSON.
    innerMap.data.loadGeoJson('google.json');

    // Add some style.
    innerMap.data.setStyle((feature) => {
        return {
            fillColor: feature.getProperty('color'),
            strokeWeight: 1,
        };
    });

    // Set mouseover event for each feature.
    innerMap.data.addListener('mouseover', (event) => {
        document.getElementById('info-box').textContent =
            event.feature.getProperty('letter');
    });
}

void init();

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;
}

#info-box {
    background-color: white;
    border: 1px solid black;
    bottom: 30px;
    height: 20px;
    padding: 10px;
    position: absolute;
    left: 30px;
}

HTML

<html>
    <head>
        <title>Data Layer: Event Handling</title>

        <link rel="stylesheet" type="text/css" href="./style.css" />
        <script type="module" src="./index.js"></script>
        <script>
            // prettier-ignore
            (g=>{var h,a,k,p="The Google Maps JavaScript API",c="google",l="importLibrary",q="__ib__",m=document,b=window;b=b[c]||(b[c]={});var d=b.maps||(b.maps={}),r=new Set,e=new URLSearchParams,u=()=>h||(h=new Promise(async(f,n)=>{await (a=m.createElement("script"));e.set("libraries",[...r]+"");for(k in g)e.set(k.replace(/[A-Z]/g,t=>"_"+t[0].toLowerCase()),g[k]);e.set("callback",c+".maps."+q);a.src=`https://maps.${c}apis.com/maps/api/js?`+e;d[q]=f;a.onerror=()=>h=n(Error(p+" could not load."));a.nonce=m.querySelector("script[nonce]")?.nonce||"";m.head.append(a)}));d[l]?console.warn(p+" only loads once. Ignoring:",g):d[l]=(f,...n)=>r.add(f)&&u().then(()=>d[l](f,...n))})({
                key: "GOOGLE_MAPS_API_KEY"
            });
        </script>
    </head>
    <body>
        <gmp-map center="-28,137" zoom="4"></gmp-map>
        <div id="info-box">?</div>
    </body>
</html>

Clone Sample

Git and Node.js are required to run this sample locally. Follow these instructions to install Node.js and NPM. You will also need a Google Maps API key.

The following commands clone the repository, install dependencies, and copy the environment file. 

  git clone https://github.com/googlemaps-samples/js-api-samples.git
  cd js-api-samples
  npm i
  cp .env.template .env

Once you copy the environment file, make sure to open the .env file and replace <Insert your own development API key here> with your actual API key before starting the sample. 

  cd samples/layer-data-event
  npm start