Converting from Backbone habits to Meteor: trigger events

Question

In Backbone, if you want to talk between models you usually do it throug events. For example, if sayHi() should be done in a Friend model rather than in a Stranger model, you'd do the following.

inside Stranger

Friend.trigger("callSayHi");

inside Friend

this.listenTo("callSayHi", function() {
  sayHi();
}

I wanted to do the same in Meteor and I thought using a Session var fitted.

inside Stranger

Session.set("callSayHi", true);

inside Friend

if (Session.get("callSayHi") {
  sayHi();
}
// Session.set("callSayHi", false); <-- PROBLEM

Let's leave out the problem of scoping (using a ReactiveVar is better, etc.) here. The problem is, to handle this situation more appropriately, I would have to set the session var at the end to false again but that would invoke sayHi() event infinitely. I feel like this kind of situation is very common. What's the Meteor way of handling it?

Might be related: https://forums.meteor.com/t/track-template-state-the-template-instance-scoped-reactive-way-instead-of-using-session-vars/3048

Answer 1

You can use a tracker, either inside or outside a template. It will rerun as soon as one of its reactive dependency change.

Example outside of a template:

Tracker.autorun(function() {
  //will be run only once when Session.get('callSayHi') is true
  if(Session.get('callSayHi') {//dependency on Session var
    sayHi();
    Session.set("callSayHi", false);
  }
});

Example inside a template:

Template.yourTemplate.onCreated(function(){
  this.autorun(function() {
    //will be run only once when Session.get('callSayHi') is true
    if(Session.get('callSayHi') {//dependency on Session var
      sayHi();
      Session.set("callSayHi", false);
    }
  });
});