location.js

function cosineDistanceBetweenPoints(lat1, lon1, lat2, lon2) {
  const R = 6371e3;
  const p1 = lat1 * Math.PI/180;
  const p2 = lat2 * Math.PI/180;
  const deltaP = p2 - p1;
  const deltaLon = lon2 - lon1;
  const deltaLambda = (deltaLon * Math.PI) / 180;
  const a = Math.sin(deltaP/2) * Math.sin(deltaP/2) +
            Math.cos(p1) * Math.cos(p2) *
            Math.sin(deltaLambda/2) * Math.sin(deltaLambda/2);
  const d = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)) * R;
  return d;
}