Animate a line | Mapbox GL JS

This example animates a line by updating a GeoJSON source on each frame.
It uses addSource to add a GeoJSON source and uses addLayer to add a line layer to the map.
When the animation begins, the data in the GeoJSON object changes, and the line appears animated on the map.
The example Update a feature in realtime uses a similar approach to create an animation.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Animate a line</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="https://api.mapbox.com/mapbox-gl-js/v3.3.0/mapbox-gl.css" rel="stylesheet">
<script src="https://api.mapbox.com/mapbox-gl-js/v3.3.0/mapbox-gl.js"></script>
<style>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<style>
    button {
        position: absolute;
        margin: 20px;
    }

    #pause::after {
        content: 'Pause';
    }

    #pause.pause::after {
        content: 'Play';
    }
</style>
<div id="map"></div>
<button id="pause"></button>
<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/streets-v12',
        center: [0, 0],
        zoom: 0.5,
        projection: 'equalEarth'
    });

    // Create a GeoJSON source with an empty lineString.
    const geojson = {
        'type': 'FeatureCollection',
        'features': [
            {
                'type': 'Feature',
                'geometry': {
                    'type': 'LineString',
                    'coordinates': [[0, 0]]
                }
            }
        ]
    };

    const speedFactor = 30; // number of frames per longitude degree
    let animation; // to store and cancel the animation
    let startTime = 0;
    let progress = 0; // progress = timestamp - startTime
    let resetTime = false; // indicator of whether time reset is needed for the animation
    const pauseButton = document.getElementById('pause');

    map.on('load', () => {
        map.addSource('line', {
            'type': 'geojson',
            'data': geojson
        });

        // add the line which will be modified in the animation
        map.addLayer({
            'id': 'line-animation',
            'type': 'line',
            'source': 'line',
            'layout': {
                'line-cap': 'round',
                'line-join': 'round'
            },
            'paint': {
                'line-color': '#ed6498',
                'line-width': 5,
                'line-opacity': 0.8
            }
        });

        startTime = performance.now();

        animateLine();

        // click the button to pause or play
        pauseButton.addEventListener('click', () => {
            pauseButton.classList.toggle('pause');
            if (pauseButton.classList.contains('pause')) {
                cancelAnimationFrame(animation);
            } else {
                resetTime = true;
                animateLine();
            }
        });

        // reset startTime and progress once the tab loses or gains focus
        // requestAnimationFrame also pauses on hidden tabs by default
        document.addEventListener('visibilitychange', () => {
            resetTime = true;
        });

        // animated in a circle as a sine wave along the map.
        function animateLine(timestamp) {
            if (resetTime) {
                // resume previous progress
                startTime = performance.now() - progress;
                resetTime = false;
            } else {
                progress = timestamp - startTime;
            }

            // restart if it finishes a loop
            if (progress > speedFactor * 360) {
                startTime = timestamp;
                geojson.features[0].geometry.coordinates = [];
            } else {
                const x = progress / speedFactor;
                // draw a sine wave with some math.
                const y = Math.sin((x * Math.PI) / 90) * 40;
                // append new coordinates to the lineString
                geojson.features[0].geometry.coordinates.push([x, y]);
                // then update the map
                map.getSource('line').setData(geojson);
            }
            // Request the next frame of the animation.
            animation = requestAnimationFrame(animateLine);
        }
    });
</script>

</body>
</html>
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