Exception in delivering result of invoking method call to template instance variable

Question

I created a templateTitle method on server side to publish some data from Mongo

Theme = new Mongo.Collection("theme");
if (Meteor.isServer) {
    Meteor.startup(function () {
        Theme.insert({template: 'booking', value: 'val_example'});
    });

    Meteor.methods({
        templateTitle: function () {
            return Theme.findOne({template: 'booking'}, {value:1});
        }
    });  
}

On the client side I try to 'subscribe' that data via calling the templateTitle method - in callback function I would like to save the retrieved value and keep it in reactive variable, but I got a type error here.

Exception in delivering result of invoking 'templateTitle': TypeError: Cannot read property 'title' of null

if (Meteor.isClient) {
    Template.booking.created = function() {
        this.title = new ReactiveVar('');
    }
    Template.booking.helpers({
        templateTitle: function(){
            Meteor.call('templateTitle', function(err, data) {
                console.log(data); //data is okey
                Template.instance().title.set(data.value); //error on title
            });
            return Template.instance().title.get();
        }
    });
}

I tried also this way, but doesn't work as well

if (Meteor.isClient) {
    Template.booking.created = function() {
        this.title = new ReactiveVar('');

        this.autorun(function () {
            Meteor.call('templateTitle', function(err, data) {
                this.title.set(data.value);
            });
        });
    }

What is wrong with the 'title' variable or the callback function in general?

Answer 1

From the Meteor Docs for Template.instance() :

The template instance corresponding to the current template helper, event handler, callback, or autorun. If there isn't one, null.

I think what's happening in this case is that you're returning the template instance for the current callback (for which there is none, so null ), not the current helper . You should be able to get around this by saving the template instance locally before you make the call to the Method, then referencing that in the callback:

if (Meteor.isClient) {
  Template.booking.created = function() {
      this.title = new ReactiveVar('');
  }
  Template.booking.helpers({
      templateTitle: function(){
          var tmplInst = Template.instance();
          Meteor.call('templateTitle', function(err, data) {
              console.log(data); //data is okey
              tmplInst.title.set(data.value); //error on title
          });
          return Template.instance().title.get();
      }
  });
}