Coffeescript to convert to latitudes and longitudes into a distance

distance.coffee

distance = (lat1, lon1, lat2, lon2) ->
  R = 6371 # km (change this constant to get miles)
  dLat = (lat2 - lat1) * Math.PI / 180
  dLon = (lon2 - lon1) * Math.PI / 180
  a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) * Math.sin(dLon / 2) * Math.sin(dLon / 2)
  c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a))
  d = R * c
  if d > 1
    return d + "km"
  else return Math.round(d * 1000) + "m"  if d <= 1
  d