Async: question: check an async.queue to see if a matching task has already been inserted?

There is no officially sanctioned way to iterate the queue. There is a q._tasks property that exposes the underlying linked list for the queue. You can either iterate the linked list, or call q._tasks.toArray().find(...) to see if your task already exists.

This is an implementation detail, so it is not documented. It might break in the future if we change how the queue works internally.

Although, as an enhancement to the queue, we could expose a q[Symbol.iterator] property for exposing an implementation-agnostic way to iterate the current items of the queue.

I would also like this feature, many other queues have this feature.
q.contains(task) would be very useful!