Calculate the distance between two geopoints in Javascript

I was working on a prototype that for an geo location based app. Originally I found the algorithm that calculates the distance between two geo points on this page http://www.movable-type.co.uk/scripts/latlong.html . and then I added a little touch up to make it easier to understand and easier to use.

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/*
*calculate the direct distance between two geopoints.
*params:
*lat1: latitude of geopoint 1
*lon1: longitude of geopoint 1
*lat2: latitude of geopoint 2
*lon2: longitude of geopoint 2
*ouput: distance between two geopoints in km.
*example:distance_between_geopoints(43.716589,-79.340686,43.883333,-79.25);
*/


function distance_between_geopoints(lat1,lon1,lat2,lon2){
R = 6371;//earth’s radius (mean radius = 6,371km);
dLat = (lat2-lat1) * Math.PI / 180;
dLon = (lon2-lon1) * Math.PI / 180;
lat1 = lat1 * Math.PI / 180;
lat2 = lat2 * Math.PI / 180;
a = Math.sin(dLat/2) * Math.sin(dLat/2) +Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2);
c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
d = R * c;
return d;
}