Redux & Redux Toolkit Course
Redux & Redux Toolkit
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Middleware Execution Flow

Definition

The exact sequential order in which multiple middlewares execute, often referred to as an 'onion' model where the action passes inward through the middlewares, hits the reducer, and the response passes outward.

Explain Like I'm New

If you have Middleware A, B, and C. The action hits A, then B, then C, then the Reducer. The Reducer updates the state. Then control flows BACKWARDS: C finishes, then B finishes, then A finishes.

Real World Example

Setting up middleware where `redux-thunk` must be executed BEFORE `redux-logger`, otherwise the logger will try to log a Function (the thunk) instead of a proper object.

Common Use Cases

  • •Debugging middleware clashes
  • •Architecting complex pipelines

Interactive Example

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Interview Questions

basic

  • Does the order in which you list your middlewares in `configureStore` matter?

intermediate

  • What is the 'Onion Model' in middleware?

Flash Cards

Question

Does order matter?

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Answer

YES. Massively. Middleware executes in the exact array order you define. `[thunk, logger]` is correct. `[logger, thunk]` will break because the logger will crash when it receives a function.

Question

Onion Model?

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Answer

A middleware wraps around the `next()` call. The code you write BEFORE `next()` executes on the way IN to the reducer. The code you write AFTER `next()` executes on the way OUT.