Haversine.js

// [JavaScript]
// Haversine formula is used to calculate distance between two coords on earth

function calculeDistance(lat1, lon1, lat2, lon2, unit){
    if ((lat1 == lat2) && (lon1 == lon2)) {
      return 0;
    }
    else {
      var radlat1 = Math.PI * lat1/180;
      var radlat2 = Math.PI * lat2/180;
      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);
      if (dist > 1) {
        dist = 1;
      }
      dist = Math.acos(dist);
      dist = dist * 180/Math.PI;
      dist = dist * 60 * 1.1515;
      if (unit=="K") { dist = dist * 1.609344 }
      if (unit=="N") { dist = dist * 0.8684 }
      return dist;
    }
}

  // Usage 

calculeDistance(50.844565, 4.354104, 48.854320, 2.338819, "K")