[Solved] How to remove dependency in Tracker

help
1

The following code loops

const route = new ReactiveVar (['login'])

Tracker.autorun(() => {
  const u = Meteor.userId()
  if (!u) {
     console.log("before", route.get())
     route.set(['login'])
     console.log("after", route.get())
  }
 })

With the following message

before ["login"]
after ["login"]
before ["login"]

This is due to ReactiveVar using pointer equality by default, the reactive var doesn’t recognize the array is already [‘login’] and updates, which triggers the autorun. Simple fix is to provide a custom equality function that computes structural equality.

const array_eq = (a, b) => {
  if (a == null && b == null) return true
  if (!a || !b) return false
  if (a.length != b.length) return false
  for (let i = 0, leni = a.length; i < leni; i++) if (a[i] != b[i]) return false
  return true
}

That said, is it possible to prevent the autorun from depending on the reactive variable ? That is, to only trigger when there is a change in Meteor.userId() and not in routes ?

2

http://docs.meteor.com/#/full/tracker_nonreactive

3

My understanding is that Tracker.nonreactive eliminates ALL dependencies. Here we want to recompute when Meteor.userId() changes but not when the reactive variable Routes changes.

4

You make the reactive call that you don’t want to track inside Tracker.nonreactive, the rest outside of it.

Tracker.autorun(function(){
  var userId = Meteor.userId(); // Depend on user id.
  var routeVal;
  Tracker.nonreactive(function() {
    routeVal = route.get(); // Don't depend on route
  });
  // Do something with routeVal & userId
})
2 Likes
5

Cool ! That’s what I missed.