haversine.js

var Distance = {
    rad: function (x) {
        return x * Math.PI / 180;
    },

    haversine: function (p1, p2) {
        var R = 637100000,
            dLat  = this.rad(p2.latitude - p1.latitude),
            dLong = this.rad(p2.longitude - p1.longitude),

            a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(this.rad(p1.latitude)) * Math.cos(this.rad(p2.latitude)) * Math.sin(dLong / 2) * Math.sin(dLong / 2),
            c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)),
            d = R * c;

        return Math.round(d);
    }
};