distance between two latitude longitude points in javascript

functiondistance(lat1, lon1, lat2, lon2)

{

  var radlat1 = Math.PI * lat1/180

  var radlat2 = Math.PI * lat2/180

  var radlon1 = Math.PI * lon1/180

  var radlon2 = Math.PI * lon2/180

  var theta = lon1-lon2

  var radtheta = Math.PI * theta/180

  var dist = Math.sin(radlat1) * Math.sin(radlat2) + Math.cos(radlat1) *   Math.cos(radlat2) * Math.cos(radtheta);

  dist = Math.acos(dist)

  dist = dist * 180/Math.PI

  dist = dist * 60 * 1.1515

  dist = dist * 1.609344 }

  return dist

}