<ul><li>Middleware in Express.js is a function that executes before the request reaches the controller or route handler.</li><li>The authMiddleware ensures only authenticated users can access /profile.</li><li>The service layer contains the business logic of the application and acts as an abstraction layer between the controller and the database.</li><li>By properly structuring the code, a maintainable, scalable, and testable application can be created.</li></ul>

Middleware vs. Service Layer: Understanding the Key Differences in Node.js

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