time.js

function animate() {
    var counter = Math.floor(100 * (Date.now() - start) / duration)
    if (counter > 100) return; // the plane is done.
    if (destination.length < 3) {
        map.getSource('airplane').setData(empty); 
        return;
    }
    map.getSource('airplane').setData({
        type: 'Feature',
        geometry: {
            type: 'Point',
            coordinates: singleArcCoords[counter]
        }
    });
    requestAnimationFrame(animate);
};
var steps = 100;
var duration = 10000; // 10 seconds
var start = Date.now();
animate();