Calculer la distance en km entre deux points

distance.js

/**
 * Find the distance between two points
 * @param  {Object} pointA {lat,lng}
 * @param  {Object} pointB {lat,lng}
 * @return {Float}        Distance
 */
function howFar(pointA, pointB) {

    var R,Dlat,Dlong,a,b,c,d;
    var rad = function(x) {return x*Math.PI/180;}

    var latB = pointB.lat,
        latA = pointA.lat,
        lngA = pointA.lng,
        lngB = pointB.lng;

    R     = 6371; // Earth radius
    dLat  = rad( LatB - LatA );
    dLong = rad( LngB - LngA );

    a = Math.sin(dLat/2) * Math.sin(dLat/2) + Math.cos(rad(LatA)) * Math.cos(rad(LatB)) * Math.sin(dLong/2) * Math.sin(dLong/2);
    c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
    d = R * c;

    return d.toFixed(3);
}

source http://www.mapanet.eu/FR/resources/Script-Distance.htm