Meteor observe subscription example

publish.js

Meteor.publish('usersImages',function(groupName){
  
  var collectionName = "user_images";
  var subscription = this;

  group = Groups.findOne({name:groupName});
  if(!group) {
    subscription.stop();
  } else {
  
    var query = {};
    query['roles._' + group._id] = {$exists:true};
    query['profile.imageFile'] = {$exists:true};

    var userHandle =  Meteor.users.find(query).observe({
      added: function(newDoc) {
        var docId = newDoc.profile.imageFile;

        var doc = UserImages.findOne({_id: docId});
        subscription.added(collectionName, docId, doc);
      },
      removed: function(oldDoc) {
        var docId = oldDoc.profile.imageFile;
        subscription.removed(collectionName, docId);
      },
      changed: function(newDoc, oldDoc) {
        var docId = newDoc.profile.imageFile;
        if (docId !== oldDoc.profile.imageFile) {
          subscription.removed(collectionName, oldDoc.profile.imageFile);
          var doc = UserImages.findOne({_id: docId});
          subscription.added(collectionName, docId, doc);
        }
      }
    });
      
    subscription.ready();
  }

  // turn off observe when client unsubscribes
  subscription.onStop(function () {
    userHandle.stop();
  });

});