Can I dispatch an action in reducer?

When working with JavaScript and Redux, you may come across a situation where you need to dispatch an action within a reducer. This can be useful in certain scenarios, but it’s important to understand the implications and potential pitfalls.

Generally, it is not recommended to dispatch actions within a reducer. Reducers are meant to be pure functions that take in the previous state and an action, and return a new state. They should not have side effects or perform any asynchronous operations.

However, there are a few workarounds if you really need to dispatch an action within a reducer. Let’s explore them:

Solution 1: Use a Middleware

The most common way to dispatch an action within a reducer is by using a middleware, such as redux-thunk or redux-saga. These middleware allow you to write asynchronous logic and dispatch actions from within your reducers.

Here’s an example of how you can use redux-thunk to dispatch an action within a reducer:

import { createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';

const initialState = {
  counter: 0
};

const reducer = (state = initialState, action) => {
  switch (action.type) {
    case 'INCREMENT':
      return { ...state, counter: state.counter + 1 };
    case 'DECREMENT':
      return { ...state, counter: state.counter - 1 };
    case 'ASYNC_ACTION':
      return { ...state, counter: state.counter + action.payload };
    default:
      return state;
  }
};

const store = createStore(reducer, applyMiddleware(thunk));

store.dispatch((dispatch) => {
  dispatch({ type: 'ASYNC_ACTION', payload: 10 });
});

console.log(store.getState().counter); // Output: 10

In this example, we use redux-thunk as a middleware to dispatch an asynchronous action within the reducer. The dispatch function is passed as an argument to the action, allowing us to dispatch additional actions.

Solution 2: Use a Side Effect Library

Another approach is to use a side effect library like redux-observable or redux-saga. These libraries provide a way to handle side effects and asynchronous operations in a separate layer, outside of the reducers.

Here’s an example using redux-observable:

import { createStore, applyMiddleware } from 'redux';
import { createEpicMiddleware, ofType } from 'redux-observable';
import { mapTo } from 'rxjs/operators';

const initialState = {
  counter: 0
};

const reducer = (state = initialState, action) => {
  switch (action.type) {
    case 'INCREMENT':
      return { ...state, counter: state.counter + 1 };
    case 'DECREMENT':
      return { ...state, counter: state.counter - 1 };
    default:
      return state;
  }
};

const incrementEpic = (action$) =>
  action$.pipe(
    ofType('INCREMENT'),
    mapTo({ type: 'ASYNC_ACTION', payload: 10 })
  );

const epicMiddleware = createEpicMiddleware();

const store = createStore(reducer, applyMiddleware(epicMiddleware));

epicMiddleware.run(incrementEpic);

store.dispatch({ type: 'INCREMENT' });

console.log(store.getState().counter); // Output: 10

In this example, we use redux-observable to handle the side effect of incrementing the counter and dispatching an asynchronous action. The createEpicMiddleware function is used to create the middleware, and the run method is called to start the epic.

Remember to carefully consider whether dispatching an action within a reducer is the best approach for your specific use case. In most cases, it’s recommended to handle side effects and asynchronous operations outside of the reducers using middleware or side effect libraries.

By following these solutions, you can dispatch actions within a reducer when necessary, while still maintaining the integrity of your Redux architecture.