JavaScript Distance Calculation

function distance(lat1, lon1, lat2, lon2, unit) {

    if ((lat1 == lat2) && (lon1 == lon2)) {

        return 0;

    } else {

        var radlat1 = Math.PI * lat1 / 180;

        var radlat2 = Math.PI * lat2 / 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);

        if (dist > 1) {

            dist = 1;

        }

        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.toFixed(2);

    }

}