How to keep my reducer pure when using Redux Promise Middleware?

Question

I'm using Redux Promise Middleware and my action creator returns an action with a promise.

Now, in the reducer, I receive the resolved promise data and I have to 'provide' the new state. I also have to do something that is not 'pure' with that data, e.g., store it in local storage.

How should I approach this situation and still keep the reducer pure? That data is obtained in middleware and the first time I get it is in reducer.

I know I can handle the promise in my action creator and access the data before dispatching the action but is there another better way?

redux-observable / redux-saga are middlewares to take care of this. — Balázs Édes
No, Redux Observable and/or Redux Saga won't take care of this. The question is about how to store data in local storage while keeping pure the reducer(s) that use said data. — Patrick

Ematipico Ematipico · Accepted Answer · 2017-06-09T15:30:34

You can create your own middleware!

You can call it localStorage-middleware for instance and you can dispatch the action before providing your data to the reducer. Your middleware will listen to that action, like dispatch(saveDataToLocalStorage(dataToSave))

How to keep my reducer pure when using Redux Promise Middleware?

1 Answers