Note that calling this function within a signal calculation even once adds a permanent, implicit dependency to that signal, on whether the signal is being observed. (As does using any job APIs directly.)
The assumption here is that if you're checking whether it's observed, it's because you only want to do certain things while it's being observed, so the signal needs to be recalculated when it starts being observed, so you can do those things. (If you need to undo or clean up those things when the signal is no-longer observed, you can register a cleanup callback via e.g. must(), or wrap them in a sub-job with start, connect, etc.)
Find out whether the active signal is being observed, or just queried.
If the return value is true, the caller is running within a signal calculation that is being observed by subscribers (such as a rule or stream listener). If the return value is false, the caller is running within a signal calculation that is not observed by any subscribers, and the signal will be recalculated whenever it transitions from unobserved to observed.
Returns
undefinedif the caller isn't running in a signal calculation.