haversine.js

/*
* Gets the distance in meters from two coordinate objects
*
* @params coord1 (object|required), coord2 (object|required)
*
* @returns int meters
*/
function distanceBetweenCoords(coord1, coord2){

    var R = 6371000; // earth's radius in meters
    var x1 = coord2.latitude - coord1.latitude;
    var dLat = x1 * Math.PI / 180;
    var x2 = coord2.longitude - coord1.longitude;
    var dLon = x2 * Math.PI / 180;
    var lat1 = coord1.latitude * Math.PI / 180;
    var lat2 = coord2.latitude * Math.PI / 180;
    var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.cos(lat1) * Math.cos(lat2) *
        Math.sin(dLon/2) * Math.sin(dLon/2);
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
    return R * c;

}