The question being asked is whether executeUpdate method performs synchronous execution of the listener function queue during its execution.
This after sending the command to the server and the server completing execution of the NOTIFY. This assumes that the server places the notification on the channel for pick-up immediately (which will not be the case within a transaction).
While the client is, IIRC, synchronous, thus the local order of operations can be controlled, the server is asynchronous and thus this test is exposed to timing issues. Maybe we need something like conn.listenSync() that blocks until a notification payload is received on the connection...?
kind of defeats the asynchronous aspect, no ?
You'd still want an asynchronous API for people but JavaScript introduced the "async/await" feature for a reason. In this case making it "sync" instead of coding up wait loop seems desirable. That said its quite possible I'm missing some existing feature as I haven't used this API at all.