watchGeoPosition.js

navigator.geolocation.watchPosition(function(g){
  if (g.coords.latitude === null && g.coords.longitude === null) return;
  var c = g.coords, l = { acc: c.accuracy };
  if (c.latitude !== null) l.lat = ~~(c.latitude*10000)/10000;
  if (c.longitude !== null)l.long = ~~(c.longitude*10000)/10000;
  if (c.speed !== null) l.speed = c.speed;
  if (c.heading !== null && !isNaN(c.heading)) l.dir = c.heading;
  if (c.altitude) { l.alt = c.altitude; l.altacc = c.altitudeAccuracy }
  console.log(l);
});