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Redux Middleware

To appreciate how thunks can help us integrate asynchronous actions into our Redux apps, let’s review the barriers to performing asynchronous operations that exist within traditional Redux. First, asynchronous logic returns promises, and store.dispatch expects to receive a plain object with a type property. Second, asynchronous operations create side effects. And so including them in our reducers would violate a core tenet of Redux, which is that reducers must be pure functions.

Redux recommends making code with side effects part of the action creation process. It would be great if we could write action creators that return thunks, which would handle our asynchronous operations, in addition to the plain objects we’ve returned from our action creators thus far.

As it turns out, redux-thunk is a middleware that lets you do exactly that. redux-thunk makes it simple for you to write asynchronous logic that interacts with the store by allowing you to write action creators that return thunks instead of objects. These thunks can perform asynchronous operations, and per the redux-thunk documentation, “can be used to delay dispatching an action” (for example, until after an API response is received), or “to dispatch an action only if certain conditions are met”.

For example, imagine we’ve written a simple counter whose reducer contains a single value, which is updated by a single reducer. Without redux-thunk we are limited to writing synchronous action creators like this one:

const increment = () => { return { type: 'counter/increment', } }

When we call dispatch(increment()), the value in our store immediately increases With redux-thunk, we can extend our counter app to accommodate asynchronous action creators, like asyncIncrement, in addition to synchronous ones.

const incrementLater = async () => { setTimeout(() => { dispatch(increment()) }, 1000) }; const asyncIncrement = () => { return incrementLater; }

redux-thunk is such a popular solution for handling asynchronous logic that it is included in Redux Toolkit. It also exists as a standalone package, but you won’t need to install redux-thunk separately if you use Redux Toolkit. This is because Redux Toolkit’s configureStore function, which you learned about in a previous lesson, will apply redux-thunk to the store by default.



Import the configureStore method from the @reduxjs/toolkit module.

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