Make data features respond to mouse events

const mapElement = document.querySelector('gmp-map') as google.maps.MapElement;
let innerMap;
let lastInteractedFeatureIds: string[] = [];
let lastClickedFeatureIds: string[] = [];
let datasetLayer;

// Note, 'globalid' is an attribute in this Dataset.
function handleClick(/* MouseEvent */ e) {
    if (e.features) {
        lastClickedFeatureIds = e.features.map(
            (f) => f.datasetAttributes['globalid']
        );
    }
    datasetLayer.style = applyStyle;
}

function handleMouseMove(/* MouseEvent */ e) {
    if (e.features) {
        lastInteractedFeatureIds = e.features.map(
            (f) => f.datasetAttributes['globalid']
        );
    }
    datasetLayer.style = applyStyle;
}

async function initMap() {
    // Request needed libraries.
    (await google.maps.importLibrary('maps')) as google.maps.MapsLibrary;

    // Get the inner map.
    innerMap = mapElement.innerMap;

    // Dataset ID for NYC park data.
    const datasetId = 'a75dd002-ad20-4fe6-af60-27cd2ed636b4';

    datasetLayer = innerMap.getDatasetFeatureLayer(datasetId);
    datasetLayer.style = applyStyle;

    datasetLayer.addListener('click', handleClick);
    datasetLayer.addListener('mousemove', handleMouseMove);

    // Map event listener.
    innerMap.addListener('mousemove', () => {
        // If the map gets a mousemove, that means there are no feature layers
        // with listeners registered under the mouse, so we clear the last
        // interacted feature ids.
        if (lastInteractedFeatureIds?.length) {
            lastInteractedFeatureIds = [];
            datasetLayer.style = applyStyle;
        }
    });
}

const styleDefault = {
    strokeColor: 'green',
    strokeWeight: 2.0,
    strokeOpacity: 1.0,
    fillColor: 'green',
    fillOpacity: 0.3,
};

const styleClicked = {
    ...styleDefault,
    strokeColor: 'blue',
    fillColor: 'blue',
    fillOpacity: 0.5,
};

const styleMouseMove = {
    ...styleDefault,
    strokeWeight: 4.0,
};

function applyStyle(/* FeatureStyleFunctionOptions */ params) {
    const datasetFeature = params.feature;

    // Note, 'globalid' is an attribute in this dataset.
    if (
        lastClickedFeatureIds.includes(
            datasetFeature.datasetAttributes['globalid']
        )
    ) {
        return styleClicked;
    }

    if (
        lastInteractedFeatureIds.includes(
            datasetFeature.datasetAttributes['globalid']
        )
    ) {
        return styleMouseMove;
    }
    return styleDefault;
}

initMap();
index.ts

const mapElement = document.querySelector('gmp-map');
let innerMap;
let lastInteractedFeatureIds = [];
let lastClickedFeatureIds = [];
let datasetLayer;
// Note, 'globalid' is an attribute in this Dataset.
function handleClick(/* MouseEvent */ e) {
    if (e.features) {
        lastClickedFeatureIds = e.features.map((f) => f.datasetAttributes['globalid']);
    }
    datasetLayer.style = applyStyle;
}
function handleMouseMove(/* MouseEvent */ e) {
    if (e.features) {
        lastInteractedFeatureIds = e.features.map((f) => f.datasetAttributes['globalid']);
    }
    datasetLayer.style = applyStyle;
}
async function initMap() {
    // Request needed libraries.
    (await google.maps.importLibrary('maps'));
    // Get the inner map.
    innerMap = mapElement.innerMap;
    // Dataset ID for NYC park data.
    const datasetId = 'a75dd002-ad20-4fe6-af60-27cd2ed636b4';
    datasetLayer = innerMap.getDatasetFeatureLayer(datasetId);
    datasetLayer.style = applyStyle;
    datasetLayer.addListener('click', handleClick);
    datasetLayer.addListener('mousemove', handleMouseMove);
    // Map event listener.
    innerMap.addListener('mousemove', () => {
        // If the map gets a mousemove, that means there are no feature layers
        // with listeners registered under the mouse, so we clear the last
        // interacted feature ids.
        if (lastInteractedFeatureIds?.length) {
            lastInteractedFeatureIds = [];
            datasetLayer.style = applyStyle;
        }
    });
}
const styleDefault = {
    strokeColor: 'green',
    strokeWeight: 2.0,
    strokeOpacity: 1.0,
    fillColor: 'green',
    fillOpacity: 0.3,
};
const styleClicked = {
    ...styleDefault,
    strokeColor: 'blue',
    fillColor: 'blue',
    fillOpacity: 0.5,
};
const styleMouseMove = {
    ...styleDefault,
    strokeWeight: 4.0,
};
function applyStyle(/* FeatureStyleFunctionOptions */ params) {
    const datasetFeature = params.feature;
    // Note, 'globalid' is an attribute in this dataset.
    if (lastClickedFeatureIds.includes(datasetFeature.datasetAttributes['globalid'])) {
        return styleClicked;
    }
    if (lastInteractedFeatureIds.includes(datasetFeature.datasetAttributes['globalid'])) {
        return styleMouseMove;
    }
    return styleDefault;
}
initMap();
index.js

/* 
 * Optional: Makes the sample page fill the window. 
 */
html,
body {
    height: 100%;
    margin: 0;
    padding: 0;
}

#attribution {
    background-color: rgba(255, 255, 255, 0.7);
    font-family: 'Roboto', 'Arial', 'sans-serif';
    font-size: 10px;
    padding: 2px;
    margin: 2px;
}
style.css

<html>
    <head>
        <title>Style a polygon data feature</title>

        <link rel="stylesheet" type="text/css" href="./style.css" />
        <script type="module" src="./index.js"></script>
        <!-- prettier-ignore -->
        <script>(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: "AIzaSyA6myHzS10YXdcazAFalmXvDkrYCp5cLc8", v: "weekly"});</script>
    </head>
    <body>
        <gmp-map
            center="40.780101, -73.967780"
            zoom="13"
            map-id="5cd2c9ca1cf05670"
            map-type-control="false">
            <div id="attribution" slot="control-block-end-inline-start">
                Data source: NYC Open Data
            </div>
        </gmp-map>
    </body>
</html>
index.html