Promises represent a calculation in progress, rather than one to occur later, which muddies the…
James DiGioia

…because streams don’t produce side effects until they’re observed, and the stream returned from the Epic is observed at the edges of the system.

But redux-observable sponsors observing midway! Not at the edges. When you do .mergeMap(() => getJSON()) it’s the .mergeMap that subscribes (hence observes) to the observable, not the edge of the system.

And observing midway does not make things imperative per-se; it’s when observing-midway causes a side-effect that makes things imperative.

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