Assuming you have an HTML element with id = "distance", you probably need this:
function getLocation(a, b, element) {
if (navigator.geolocation) {
navigator.geolocation.getCurrentPosition(function (position) {
lat = position.coords.latitude;
lng = position.coords.longitude;
var d = getDistanceFromLatLonInKm(a,b,lat, lng);
document.getElementById(element).innerHTML = d;
});
}
}
function getDistanceFromLatLonInKm(lat_origin, lon_origin, lat_pos, lon_pos) {
var R = 6371;
var dLat = deg2rad(lat_pos - lat_origin);
var dLon = deg2rad(lon_pos - lon_origin);
var a =
Math.sin(dLat / 2) * Math.sin(dLat / 2) +
Math.cos(deg2rad(lat_origin)) * Math.cos(deg2rad(lat_pos)) *
Math.sin(dLon / 2) * Math.sin(dLon / 2)
;
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
var d = R * c;
return d;
}
function deg2rad(deg) {
return deg * (Math.PI/180)
}
getLocation(45.123, 12.123, 'distance');