Created by: igncp
Seems that the drainDelay setting is not present in the docs or types definitions.
Keeping it private may be intentional, or it could be a temporal API, but wasn't sure, I could also add a comment in lib/queue.js if that is the case.
Also, the explanation I added may not be complete.
If approved I could update the TypeScript definitions too: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/625451856aaebad9b6446e3827650f4f2e482d4e/types/bull/index.d.ts#L59
Cheers