What is the timing of update of Meteor.connection._lastSessionId?


I want to update something depending with Meteor.connection._lastSessionId.
I tried

Tracker.autorun ->
    unless Meteor.status().connected
    something Meteor.connection._lastSessionId
    # or 
    setTimeout ->
        something Meteor.connection._lastSessionId
    , 0

Both failed and I found that it needs 100ms delay of setTimeout to get a correct result.

Is there reactive _lastSessionId or a way to know updating _lastSessionId?

I might understand that _lastSessionId is not connection id, it is namely last session id.

So I checked it in the callback of some Meteor.call.