Can this function be garbage-collected?

Question

Consider this piece of cake... ehm, code:

'use strict'

function doWork () {
  return new Promise(function (resolve, reject) {
    // work work work...
    // Done! But... where's the resolve() ???
  })
}

doWork().then(function doMoreWork () {
  // Some more work to do...
})

Once the function in the Promise's constructor finishes...

1. Is the Promise object garbage-collectible?
2. Is doMoreWork() garbage-collectible?

My guess is that doMoreWork() cannot be GC-ed directly because the Promise keeps a reference to it, but once the promise's body finishes and returns the execution context to the upper (?) scope, the stack unwinds (because there is no more statements here to be executed) and the Promise becomes unreachable, thus being garbage-collectible.

Can you confirm that my understanding of this topic is correct?

How could I empirically observe this behaviour? In other words, how can I monitor what objects are being GC-ed and when? I develop purely in Node.js, if that makes any difference.

Answer 1

There is nothing keeping reference to the promise so it will be garbage collected. The promise is the only thing keeping reference to the function doMoreWork so it will be garbage collected too.

How could I empirically observe this behaviour? In other words, how can I monitor what objects are being GC-ed and when? I develop purely in Node.js, if that makes any difference.

The GC in V8 never necessarily collects an object. For instance if this is your whole program, it would be a waste of time to run any GC in the first place.