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Update a feature in realtime

Change an existing feature on your map in real-time by updating its data.

<!DOCTYPE html>
<html lang="en">
<head>
    <title>Update a feature in realtime</title>
    <meta property="og:description" content="Change an existing feature on your map in real-time by updating its data." />
    <meta charset='utf-8'>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel='stylesheet' href='https://unpkg.com/maplibre-gl@4.4.0/dist/maplibre-gl.css' />
    <script src='https://unpkg.com/maplibre-gl@4.4.0/dist/maplibre-gl.js'></script>
    <style>
        body { margin: 0; padding: 0; }
        html, body, #map { height: 100%; }
    </style>
</head>
<body>
<div id="map"></div>

<script src="https://d3js.org/d3.v3.min.js" charset="utf-8"></script>
<script>
    const map = new maplibregl.Map({
        container: 'map',
        style:
            'https://api.maptiler.com/maps/streets/style.json?key=get_your_own_OpIi9ZULNHzrESv6T2vL',
        zoom: 0
    });

    map.on('load', () => {
        // We use D3 to fetch the JSON here so that we can parse and use it separately
        // from GL JS's use in the added source. You can use any request method (library
        // or otherwise) that you want.
        d3.json(
            'https://maplibre.org/maplibre-gl-js/docs/assets/hike.geojson',
            (err, data) => {
                if (err) throw err;

                // 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});
                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 = window.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>