Collection re publish when field gets updated

1

This code has a collection in /lib/collection.js “HeaderLabelCol” with a server method which inserts a new document per userId, another server code updates this document’s field named headerLabel and I wish to re publish the document so that this client’s template gets updated with the new value of the headerLabel field.

I don’t understand fully what this code is doing but able to more or less understand most of it. I need your help. Thanks

//client.js

Template.header.helpers({
  headerLabel: function () {
    var userId = Meteor.userId();
    if (userId) {
      Meteor.call('getHeaderLabel', userId, function (err, res) {
        if (!err) {
          Session.set('headerLabel', res);
        }
      });
      return Session.get('headerLabel');
    } else {
      return 'Please login'
    }
  }
});

// lib/collection.js
HeaderLabelCol = new Mongo.Collection(‘headerLabelCol’);

// server.js

Meteor.publish('headerLabelCol', function (userId) {
  var self = this;
  var handle = HeaderLabelCol.find({headerLabel: {$in: [self.userId]}}).observeChanges({
    changed: function (id, fields) {
       self.update('headerLabelCol', oldValue, fields.headerLabel.value);
     }
   });
  self.ready();
  self.onStop(function () {
  handle.stop();
  });
});

  getHeaderLabel: function (userId) {
    if (userId) {
      var result = HeaderLabelCol.findOne({userId: userId});
      if (result) {
         return result.headerLabel;
       }
    }
  }