get distance between two coordinates

gistfile1.js

function distance(obj) {
  var R = 6371; // km
  var dLat = (obj.lat2 - obj.lat1) * Math.PI / 180;
  var dLon = (obj.lon2 - obj.lon1) * Math.PI / 180;
  var lat1 = obj.lat1 * Math.PI / 180;
  var lat2 = obj.lat2 * Math.PI / 180;

  var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
  Math.sin(dLon / 2) * Math.sin(dLon / 2) * Math.cos(lat1) * Math.cos(lat2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var km = R * c;
  var mi = km * 0.621371;

  return {
    km: km,
    mi: mi
  };
}