service-layer-extractor

To refactor fat controllers into a service layer, you extract business logic out of route handlers into dedicated, testable services with clean boundaries. This process provides service interfaces, folder structure, testing strategy, and a migration plan to ensure separation of concerns.

The best way to separate business logic from route handlers for testability is implementing a service layer with dependency injection. This architectural principle divides responsibilities between routing, business logic, and data access, enabling unit testing independently of HTTP concerns.

Dependency injection improves code maintainability in a service layer by facilitating cleaner management of service dependencies. This architectural pattern ensures clear boundaries between components, making the codebase easier to test, manage, and update without tightly coupling modules.

Yes, you can use this refactoring approach for a large Express.js application with mixed business logic. It specifically addresses monolithic code blocks by extracting business logic from controllers into a dedicated service layer, improving code organization and testability.

A service layer migration plan includes service interfaces, folder structure, testing strategy, and migration steps for applications with fat controllers. It satisfies architectural principles of separation of concerns while promoting maintainable, testable codebases throughout the transition.