Animate a line

Animate a line by updating a GeoJSON source on each frame.
<!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' />
<script src='https://api.tiles.mapbox.com/mapbox-gl-js/v1.2.1/mapbox-gl.js'></script>
<link href='https://api.tiles.mapbox.com/mapbox-gl-js/v1.2.1/mapbox-gl.css' rel='stylesheet' />
<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>
mapboxgl.accessToken = '<your access token here>';
var map = new mapboxgl.Map({
container: 'map',
style: 'mapbox://styles/mapbox/streets-v11',
center: [0, 0],
zoom: 0.5
});
 
// Create a GeoJSON source with an empty lineString.
var geojson = {
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"geometry": {
"type": "LineString",
"coordinates": [
[0, 0]
]
}
}]
};
 
var speedFactor = 30; // number of frames per longitude degree
var animation; // to store and cancel the animation
var startTime = 0;
var progress = 0; // progress = timestamp - startTime
var resetTime = false; // indicator of whether time reset is needed for the animation
var pauseButton = document.getElementById('pause');
 
map.on('load', function() {
 
// add the line which will be modified in the animation
map.addLayer({
'id': 'line-animation',
'type': 'line',
'source': {
'type': 'geojson',
'data': geojson
},
'layout': {
'line-cap': 'round',
'line-join': 'round'
},
'paint': {
'line-color': '#ed6498',
'line-width': 5,
'line-opacity': .8
}
});
 
startTime = performance.now();
 
animateLine();
 
// click the button to pause or play
pauseButton.addEventListener('click', function() {
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', function() {
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 {
var x = progress / speedFactor;
// draw a sine wave with some math.
var 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-animation').setData(geojson);
}
// Request the next frame of the animation.
animation = requestAnimationFrame(animateLine);
}
});
</script>
 
</body>
</html>