haversine.js

/*  
  This script is pretty basic, but if you use it, please let me know.  Thanks!
  Andrew Hedges, andrew(at)hedges(dot)name
  
  */
var Haversine = {
  Rm : 3961, // mean radius of the earth (miles) at 39 degrees from the equator
  Rk : 6373, // mean radius of the earth (km) at 39 degrees from the equator

  // convert degrees to radians
  deg2rad : function (deg) {
    var rad = deg * Math.PI / 180; // radians = degrees * pi/180
    return rad;
  },

  // round to the nearest 1/1000
  round : function (x) {
    return Math.round(x * 1000) / 1000;
  },

  /* main function */
  findDistance : function (lat1, lon1, lat2, lon2) {
    var t1, n1, t2, n2, dlat, dlon, a, c, dm, dk, mi, km;

    // get values for lat1, lon1, lat2, and lon2
    t1 = lat1;
    n1 = lon1;
    t2 = lat2;
    n2 = lon2;

    // convert coordinates to radians
    lat1 = Haversine.deg2rad(t1);
    lon1 = Haversine.deg2rad(n1);
    lat2 = Haversine.deg2rad(t2);
    lon2 = Haversine.deg2rad(n2);

    // find the differences between the coordinates
    dlat = lat2 - lat1;
    dlon = lon2 - lon1;

    // here's the heavy lifting
    a  = Math.pow(Math.sin(dlat/2), 2) + Math.cos(lat1) * Math.cos(lat2) * Math.pow(Math.sin(dlon/2), 2);
    c  = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); // great circle distance in radians
    dm = c * Haversine.Rm; // great circle distance in miles
    dk = c * Haversine.Rk; // great circle distance in km

    // round the results down to the nearest 1/1000
    mi = Haversine.round(dm);
    km = Haversine.round(dk);

    // display the result
    console.log(mi + 'miles');
    console.log(km + 'km');
  }
};