averageVelocity.js

const totalDistance = waypoints => waypoints.map(w => calculateDistance(w)).reduce((acc, d) => acc + d, 0);

/* Average velocity in m/s between any (consecutive) waypoints */
const avgVelocity = wayPoints => {

  if(wayPoints.length < 2) {
    return 0;
  }
  
  const first = wayPoints[0];
  const [last] = wayPoints.slice(-1);
  const elapsedTime = last.time - first.time;
  
  return totalDistance(wayPoints) / elapsedTime;
}