How do I make sure my subscription is ready before looking for it inside the helper?

I want to do something very simple, namely turn the value of a field in my database into a variable in my helper. The document looks like this:

{
  hero: "Simon Belmont",
  universe: "Castlevania",
  items: ["Whip", "Cross", "Oak Stake"]
}

      

        
        
        
      

    

In a helper, I want to do something similar to this:

var selectedHeroId = Session.get('whichHeroSelected')
var heroItems = Heroes.findOne({_id: selectedHero}).items

      

        
        
        
      

    

This, however, proved to be very fickle. Sometimes he complains that he is items

not defined. Oddly enough, it works when I call a variable items

, but not when I call it heroItems

or itemsArray

.

So, I'm looking for a way to make sure that it is Heroes

signed before looking for things in the database. I subscribe to it in the Iron Router feature by the waitOn

way.