dunno if it can help but David Walsh wrote about something similar few days ago.
It's not really checking against a variable - or more precisely, the result of a function call - but can be useful to decide if await a function or not (instead of adding a then to the result)
checking the constructor.name of a function returns "AsyncFunction" instead of "Function" if that is indeed an async one :-)
That's a nice bit of intel. In our case we wanted to capture both promises and async, as we're still using both. But I'm going to keep this one in my head for sure 😃
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