[jcheng]

> And closures for things like callbacks for AJAX etc. -- these are generally fine, because once the AJAX returns and the callback function finishes executing, then once the AJAX object gets garbage-collected, the callback will too, and its closure.

I'm not sure that this is as fine as you think it is. Those callbacks may invoke other callbacks, which may access any variable that's in its lexical scope, and as the Meteor bug shows, you may be inadvertently holding on to not the callback itself, but the environment it lives in.

I think this may be exacerbated in promise-oriented Node.js code since it is so easy to take a promise and stash it in a list or object (which we do in my current project[0], and indeed this code has been the source of memory leaks in the past and may still be leaking).

[0] https://github.com/rstudio/shiny-server/blob/master/lib/sche...