Update a feature in realtime
Change an existing feature on your map in realtime by updating its data
<!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8' />
    <title></title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.34.0/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.34.0/mapbox-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 src='//d3js.org/d3.v3.min.js' charset='utf-8'></script>
<script>
mapboxgl.accessToken = '<your access token here>';
var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/satellite-v9',
    zoom: 0
});

map.on('load', function () {
    // 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://www.mapbox.com/mapbox-gl-js/assets/data/hike.geojson', function(err, data) {
        if (err) throw err;

        // save full coordinate list for later
        var 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
        var i = 0;
        var timer = window.setInterval(function() {
            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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