javascript compute heading on too points

1// Converts from degrees to radians.
2function toRadians(degrees) {
3  return degrees * Math.PI / 180;
4};
5 
6// Converts from radians to degrees.
7function toDegrees(radians) {
8  return radians * 180 / Math.PI;
9}
10
11
12function bearing(startLat, startLng, destLat, destLng){
13  startLat = toRadians(startLat);
14  startLng = toRadians(startLng);
15  destLat = toRadians(destLat);
16  destLng = toRadians(destLng);
17
18  y = Math.sin(destLng - startLng) * Math.cos(destLat);
19  x = Math.cos(startLat) * Math.sin(destLat) -
20        Math.sin(startLat) * Math.cos(destLat) * Math.cos(destLng - startLng);
21  brng = Math.atan2(y, x);
22  brng = toDegrees(brng);
23  return (brng + 360) % 360;
24}