dispatch while render?

[arcanis]

The React documentation suggests that, in some cases, it's better to call setState from within render than to do it from within an effect. Is it true as well from dispatch?

[markerikson]

No, never.

The use case of calling setState() while rendering only works because React special-cases that exact behavior. If it detects that you tried to do a setState() while rendering, it queues up that state update and immediately, synchronously re-runs the rendering for that component before continuing. That means that conceptually this can sorta be seen as "not actually a side effect", because the behavior is never visible to the outside world (similar to creating a new object/array in a function, mutating it, and then returning it - no one else ever saw it being mutated, so it's okay in that case).

With Redux, on the hand, dispatching an action while rendering is most definitely a side effect. The Redux store gets updated immediately, and that is an externally visible (across the app) change.

Moreover, dispatching actions normally causes Redux-connected components to queue a re-render... and React will throw errors if component B has a render queued up while it's in the middle of rendering component A.

So, no, don't ever dispatch actions in the middle of rendering a React component :)