Update style of individual feature from single geoJSON source on Mapbox map, when clicked - mapbox

Question

I'm working with Mapbox GL JS to plot geoJSON data on a map using their external geoJSON example as a starting point. The geoJSON file contains lots of features which are plotted as individual markers on the same layer. I would like to highlight the clicked marker by changing its colour from red to blue. I have adapted the example to show a pop-up with the point id when clicked (just as a proof of concept that the markers can fire events when clicked), however, I'm struggling to find a way to change the styling of the individual clicked marker.
The code is currently as follows:
mapboxgl.accessToken = 'pk.eyJ1IjoiZGFuYnJhbWFsbCIsImEiOiJjbDB3ODFveHYxOG5rM2pubWpwZ2R1Y2xuIn0.yatzJHqBTjQ6F3DHASlriw';
const map = new mapboxgl.Map({
container: 'map', // container ID
style: 'mapbox://styles/mapbox/satellite-v9', // style URL
zoom: 7, // starting zoom
center: [138.043, 35.201] // starting center
});
map.on('load', () => {
map.addSource('earthquakes', {
type: 'geojson',
data: 'https://docs.mapbox.com/mapbox-gl-js/assets/earthquakes.geojson'
});
map.addLayer({
'id': 'earthquakes-layer',
'type': 'circle',
'source': 'earthquakes',
'paint': {
'circle-radius': 8,
'circle-stroke-width': 2,
'circle-color': 'red',
'circle-stroke-color': 'white'
}
});
});
map.on('click', 'earthquakes-layer', (e) => {
new mapboxgl.Popup()
.setLngLat(e.lngLat)
.setHTML('Id: ' + e.features[0].properties.id)
.addTo(map);
});
Here is a codepen: https://codepen.io/danb1/pen/BaYjOyx
Is it the case that it's actually not possible to use this approach, and instead each feature from the geoJSON file needs to be plotted as a separate layer? I'm struggling to find any examples of this and am not able to modify the geoJSON source — it has to come from one single file (rather than loading multiple geoJSON files separately on separate layers).

Answer 1

This is possible using feature-state. The first thing to do is to ensure the layer data contains ids for each feature (in the example the source data doesn't so we need to add generateId: true to the map.addSource method).
We then need to add mousemove and mouseleave events to the map to store the moused-over feature id (if there is one, i.e. if the mouse is hovering over a feature):
let hoveredEarthquakeId = null;
map.on('mousemove', 'earthquakes-layer', (e) => {
map.getCanvas().style.cursor = 'pointer';
if (e.features.length > 0) {
map.setFeatureState(
{ source: 'earthquakes', id: e.features[0].id },
{ hover: true }
);
hoveredEarthquakeId = e.features[0].id;
}
});
map.on('mouseleave', 'earthquakes-layer', () => {
map.getCanvas().style.cursor = '';
if (hoveredEarthquakeId !== null) {
map.setFeatureState(
{ source: 'earthquakes', id: hoveredEarthquakeId },
{ hover: false }
);
}
hoveredEarthquakeId = null;
});
Finally, in the layer properties, the colour setting of the circle needs to be updated to reflect the hover value stored against the feature:
'circle-color': [
'case',
['boolean', ['feature-state', 'hover'], false],
'#00f',
'#f00'
],
The final thing can be seen in the modified pen. There is also a MapBox tutorial covering this kind of thing in a slightly more complicated way, which I hadn't come across until now: https://docs.mapbox.com/help/tutorials/create-interactive-hover-effects-with-mapbox-gl-js/.