This series is about code in various languages that will calculate the distance between two latitudes and longitudes. This article is for the Javascript code.

Code courtsey : GeoDataSource

/*::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/
/*::                                                             :*/
/*::  This routine calculates the distance between two           :*/
/*::  points (given the latitude/longitude of those points).     :*/
/*::  It is being used to calculate the distance between two     :*/
/*::  locations using GeoDataSource(TM) Products                 :*/
/*::                                                             :*/
/*::  Definitions:                                               :*/
/*::    South latitudes are negative,                            :*/
/*::    east longitudes are positive                             :*/
/*::                                                             :*/
/*::  Passed to function:                                        :*/
/*::    lat1, lon1 = Latitude and Longitude of point 1           :*/
/*::                 (in decimal degrees)                        :*/
/*::    lat2, lon2 = Latitude and Longitude of point 2           :*/
/*::                 (in decimal degrees)                        :*/
/*::    unit = the unit you desire for results                   :*/
/*::           where: 'M' is statute miles                       :*/
/*::                  'K' is kilometers (default)                :*/
/*::                  'N' is nautical miles                      :*/
/*::  Worldwide cities and other features databases with         :*/
/*::  latitude longitude are available at                        :*/
/*::  http://www.geodatasource.com                               :*/ 
/*::                                                             :*/
/*::  For enquiries, please contact [email protected]      :*/
/*::                                                             :*/
/*::  Official Web site: http://www.geodatasource.com            :*/
/*::                                                             :*/
/*::         GeoDataSource.com (C) All Rights Reserved 2014      :*/
/*::                                                             :*/
/*::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::*/

function distance(lat1, lon1, lat2, lon2, unit) 
{
	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;
	if (unit=="K") { dist = dist * 1.609344 }
	if (unit=="N") { dist = dist * 0.8684 }
	return dist;
}        

document.write(distance(32.9697, -96.80322, 29.46786, -98.53506, "K") + " Kilometers");