haversine_salvador (v6)

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = deg2rad(lat2 - lat1);  // deg2rad below
  var dLon = deg2rad(lon2 - lon1);
  var a = 
     Math.sin(dLat/2) * Math.sin(dLat/2) + 
     Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * 
     Math.sin(dLon/2) * Math.sin(dLon/2);

  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
  var d = R * c; // Distance in km
  return d;
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371;
  var dLat = deg2rad(lat2 - lat1);
  var dLon = deg2rad(lon2 - lon1);
  var a = 
     0.5 - Math.cos(dLat)/2 + 
     Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * 
     (1 - Math.cos(dLon))/2;

  return R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = (lat2 - lat1) * Math.PI / 180;  // deg2rad below
  var dLon = (lon2 - lon1) * Math.PI / 180;
  var a = 
     0.5 - Math.cos(dLat)/2 + 
     Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) * 
     (1 - Math.cos(dLon))/2;

  return R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = (lat2 - lat1) * Math.PI / 180;  // deg2rad below
  var dLon = (lon2 - lon1) * Math.PI / 180;
  var a = 
     0.5 - Math.cos(dLat)/2 + 
     Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) * 
     (1 - Math.cos(dLon))/2;

  return R * 2 * Math.asin(Math.sqrt(a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var deg2rad = Math.PI / 180;
  lat1 *= deg2rad;
  lon1 *= deg2rad;
  lat2 *= deg2rad;
  lon2 *= deg2rad;
  var diam = 12742; // Diameter of the earth in km (2 * 6371)
  var dLat = lat2 - lat1;
  var dLon = lon2 - lon1;
  var a = (
     (1 - Math.cos(dLat)) + 
     (1 - Math.cos(dLon)) * Math.cos(lat1) * Math.cos(lat2)
  ) / 2;

  return diam * Math.asin(Math.sqrt(a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var deg2rad = 0.017453292519943295; // === Math.PI / 180
  var cos = Math.cos;
  lat1 *= deg2rad;
  lon1 *= deg2rad;
  lat2 *= deg2rad;
  lon2 *= deg2rad;
  var diam = 12742; // Diameter of the earth in km (2 * 6371)
  var dLat = lat2 - lat1;
  var dLon = lon2 - lon1;
  var a = (
     (1 - cos(dLat)) + 
     (1 - cos(dLon)) * cos(lat1) * cos(lat2)
  ) / 2;

  return diam * Math.asin(Math.sqrt(a));
}

distance(48, -122, 49, -121);

function distance(lat1, lon1, lat2, lon2) {
  var deg2rad = 0.017453292519943295; // === Math.PI / 180
  var cos = Math.cos;
  lat1 *= deg2rad;
  lon1 *= deg2rad;
  lat2 *= deg2rad;
  lon2 *= deg2rad;
  var a = (
     (1 - cos(lat2 - lat1)) + 
     (1 - cos(lon2 - lon1)) * cos(lat1) * cos(lat2)
  ) / 2;

  return 12742 * Math.asin(Math.sqrt(a)); // Diameter of the earth in km (2 * 6371)
}

distance(48, -122, 49, -121);