redux - All reducers will be invoked when an action is dispatched?

Question

I am using combineReducers to combine all the reducers to create the store, does it mean that any action dispatched from any view will trigger all the reducers being invoked to check the action type？Is it kind of low efficiency?

Or I don't fully understand the redux design principle？

Answer 1

Yes, that is correct.

However one option you have to optimize this behaviour (suggested from the Redux docs) is to use 'reselect' https://github.com/rackt/reselect

Reselect basically allows you to create memoized selectors, whereby you can say that props A depends on state B and state C, and therefore only recompute props A if state B or state C changes.

Notice that this will still trigger all of the reducers to run (and go through the switch statement to see if the action might apply to them) - I believe there is no way around this behaviour. Using reselect however means that your top level component will only receive a prop/state change if there was an actual change that affects that state, rather than triggering a change every time and making React re-render everything, even when the change had no effect because it was somewhere unrelated. (The readme in reselect explains better)