Update a feature in realtime | Mapbox GL JS

This example shows how to change an existing feature on a map by updating its data.

It shows the progression of a path by adding new coordinates to a feature in a line layer. This approach is useful for visualizing real-time data sources.

Calling setData begins a new render cycle which makes the updates appear in real time without explicitly creating an animation. panTo then follows the leading edge of the line to keep it on screen.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Update a feature in realtime</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="https://api.mapbox.com/mapbox-gl-js/v3.0.1/mapbox-gl.css" rel="stylesheet">
<script src="https://api.mapbox.com/mapbox-gl-js/v3.0.1/mapbox-gl.js"></script>
<style>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<div id="map"></div>
 
<script>
	// TO MAKE THE MAP APPEAR YOU MUST
	// ADD YOUR ACCESS TOKEN FROM
	// https://account.mapbox.com
	mapboxgl.accessToken = 'YOUR_MAPBOX_ACCESS_TOKEN';
const map = new mapboxgl.Map({
container: 'map',
// Choose from Mapbox's core styles, or make your own style with Mapbox Studio
style: 'mapbox://styles/mapbox/satellite-v9',
zoom: 0
});
 
map.on('load', async () => {
// We fetch the JSON here so that we can parse and use it separately
// from GL JS's use in the added source.
const response = await fetch(
'https://docs.mapbox.com/mapbox-gl-js/assets/hike.geojson'
);
const data = await response.json();
// save full coordinate list for later
const coordinates = data.features[0].geometry.coordinates;
 
// start by showing just the first coordinate
data.features[0].geometry.coordinates = [coordinates[0]];
 
// add it to the map
map.addSource('trace', { type: 'geojson', data: data });
map.addLayer({
'id': 'trace',
'type': 'line',
'source': 'trace',
'paint': {
'line-color': 'yellow',
'line-opacity': 0.75,
'line-width': 5
}
});
 
// setup the viewport
map.jumpTo({ 'center': coordinates[0], 'zoom': 14 });
map.setPitch(30);
 
// on a regular basis, add more coordinates from the saved list and update the map
let i = 0;
const timer = setInterval(() => {
if (i < coordinates.length) {
data.features[0].geometry.coordinates.push(coordinates[i]);
map.getSource('trace').setData(data);
map.panTo(coordinates[i]);
i++;
} else {
window.clearInterval(timer);
}
}, 10);
});
</script>
 
</body>
</html>

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