Great question — answering as the UphillTech team:
No such synchronous inspection API exists for native JavaScript promises. It is impossible to do this with native promises. The specification does not specify such a method. Userland libraries can do this, and if you're targeting a specific engine (like v8) and have access to platform code (that is, you can write code in core ) then you can use specific tools (like private symbols) to achieve this. That's super specific though and not in userland.
Full answer by Benjamin Gruenbaum: https://stackoverflow.stackexchange.com/a/30564128 (CC BY-SA 3.0).
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