Check out a free preview of the full Meteor course:
The "Tracker" Lesson is part of the full, Meteor course featured in this preview video. Here's what you'd learn in this lesson:

Chris goes under the hood of Meteor’s reactive nature to better explain how function like helpers are re-run. This is facilitated by a Meteor package called Tracker. The Tracker package creates a computation, or function-wrapper, which re-runs a function whenever it’s invalidated.

Get Unlimited Access Now