set monitoringIntervalId to be able to stop monitoring

monitoringIntervalId should not be part of some "network state" object(something we've talked about we need to have), we need to make sure we stop monitoring before deleting the object.

I really think we should be using more assertions, if that even does anything in js. I haven't seen us using assertions in our code though, I'm not sure why.

If we has more tests maybe we could check there are no assertions and then they'd be useful.