gistfile1.js

var loggedIn = false;
Meteor.autorun(function() {
  var user = Meteor.user();
  if (user) {
    if (!loggedIn) {
      loggedIn = true;
      /* Login callback */
    }
  } else {
    if (loggedIn) {
      loggedIn = false;
      /* Logout callback */
    }
  }
});