Writing Custom Middleware

One of the powerful features of Redux is the ability to create custom middleware functions. Custom middleware allows us to perform specific tasks before an action reaches the reducer.

As a senior engineer with experience in Java backend development and Spring Boot, you may find the concept of middleware similar to request interceptors or filters in Spring Boot. In Redux, middleware functions intercept actions and can perform additional logic such as logging, making an API call, or dispatching a different action.

To create a custom middleware function, we can follow the pattern of store => next => action => { /* custom logic */ }. This pattern is known as currying, where each arrow function consumes and returns another arrow function.

Here is an example of a custom middleware function that logs information about dispatched actions:

1const loggerMiddleware = store => next => action => {
2  console.log('Dispatching:', action);
3  const result = next(action);
4  console.log('New State:', store.getState());
5  return result;
6};