Problem Statement
How do you create custom Redux middleware and when would you need one?
Explanation
Custom middleware follows the pattern store goes to next goes to action arrow, where you can inspect the action, call next with action to pass it along, dispatch other actions, access state with store.getState, or add side effects like logging or analytics. You would create custom middleware for cross-cutting concerns like authentication token injection, request/response logging, crash reporting, analytics tracking, action validation, or implementing complex side effect patterns not covered by existing middleware. The middleware receives the store API with dispatch and getState, the next middleware function, and the action, giving you full control over action flow.
