1.js

navigator.geolocation.getCurrentPosition(function (position) {
  console.log(“I am located at: “ + position.coords.latitude + “, “ + position.coords.longitude);
});

navigator.geolocation.watchPosition(function (position) {
  console.log(“I am now located at: “ + position.coords.latitude + “, “ + position.coords.longitude);
});

2.js

calculateDistance = function(lat1, lon1, lat2, lon2) {
  var R, a, c, d, dLat, dLon;
  R = 6371;
  dLat = (lat2 - lat1).toRad();
  dLon = (lon2 - lon1).toRad();
  a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
  c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  d = R * c;
  return d;
};

Number.prototype.toRad = function() {
  return this * Math.PI / 180;
};

3.js

///////////////////////////////////////////////////
// Client code (JavaScript)
///////////////////////////////////////////////////
var uuid = PUBNUB.uuid();

// PubNub and application initialization

pubnub.subscribe({
  channel: uuid,
  callback: function (data) {
    
  }
});

// Do something with the nodes

navigator.geolocation.getCurrentPosition(function (position) {
  var currentPos = position;

  pubnub.publish({
    channel: 'getNodes',
    message: {
      name: 'AUser',
      uuid: uuid,
      location: {
        latitude: currentPos.coords.latitude,
        longitude: currentPos.coords.longitude
      }
    }
  });
});

///////////////////////////////////////////////////
// Server code (JavaScript, NodeJS)
///////////////////////////////////////////////////
pubnub.subscribe({
  channel: 'getNodes',
  callback: function (data) {
    // Find the nodes the user is in using data.lat and data.long
    var insideNodes = findInsideNodes(data.lat, data.long);
    
    pubnub.publish({
      channel: data.uuid,
      message: {
        type: 'getNodes',
        inside: insideNodes
      }
    });
  }
});

No esta completo el ejemplo en el blog de PubNub:
https://www.pubnub.com/blog/2013-08-13-building-real-time-geolocation-apps-with-javascript-and-pubnub/