Create a hover effect | UNL Map JS Docs

Use events and feature states to create a per feature hover effect.

Note

If you want to test this example, edit it in JSFiddle or CodePen and replace the "YOUR-OWN-API-KEY" and "YOUR-OWN-VPM-ID" placeholders with your actual api key and vpm id.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Create a hover effect</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<script src="https://unpkg.com/unl-map-js@0.1.5/lib/unl-map-js.js"></script>
<link href="https://unpkg.com/unl-map-js@0.1.5/lib/unl-map-js.css" rel="stylesheet" />
<link
href="https://unpkg.com/maplibre-gl@2.1.9/dist/maplibre-gl.css"
rel="stylesheet"
/>
<style>
	body { margin: 0; padding: 0; }
	#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<div id="map"></div>
<script>
var map = new UnlSdk.Map({
container: "map",
apiKey: "YOUR-OWN-API-KEY",
vpmId: "YOUR-OWN-VPM-ID",
center: [-100.486052, 37.830348],
zoom: 2,
});
var hoveredStateId = null;
 
map.on("load", function () {
map.addSource("states", {
type: "geojson",
data: "https://u-n-l.github.io/unl-map-js-docs/assets/us_states.geojson",
});
 
// The feature-state dependent fill-opacity expression will render the hover effect
// when a feature's hover state is set to true.
map.addLayer({
id: "state-fills",
type: "fill",
source: "states",
layout: {},
paint: {
"fill-color": "#627BC1",
"fill-opacity": [
"case",
["boolean", ["feature-state", "hover"], false],
1,
0.5,
],
},
});
 
map.addLayer({
id: "state-borders",
type: "line",
source: "states",
layout: {},
paint: {
"line-color": "#627BC1",
"line-width": 2,
},
});
 
// When the user moves their mouse over the state-fill layer, we'll update the
// feature state for the feature under the mouse.
map.on("mousemove", "state-fills", function (e) {
if (e.features.length > 0) {
if (hoveredStateId) {
map.setFeatureState(
{ source: "states", id: hoveredStateId },
{ hover: false }
);
}
hoveredStateId = e.features[0].id;
map.setFeatureState(
{ source: "states", id: hoveredStateId },
{ hover: true }
);
}
});
 
// When the mouse leaves the state-fill layer, update the feature state of the
// previously hovered feature.
map.on("mouseleave", "state-fills", function () {
if (hoveredStateId) {
map.setFeatureState(
{ source: "states", id: hoveredStateId },
{ hover: false }
);
}
hoveredStateId = null;
});
});
</script>
 
</body>
</html>