fn-args-deps

Enforce explicit dependency injection in TypeScript by applying the fn(args, deps) pattern, which replaces business-logic classes with pure functions. This requires defining per-function dependency types and wiring collaborators at the boundary to ensure clear, testable inputs.

The best way to structure TypeScript functions for unit testing is using the fn(args, deps) pattern. By passing per-call arguments and long-lived dependencies explicitly, you create small, pure functions that avoid hidden couplings and god objects, making them highly testable.

To wire dependencies at the application boundary, define a per-function deps type and implement the function using the fn(args, deps) signature. Compose these dependencies once at the edges of your application so request handlers invoke the function with the correct collaborators.

You need per-function dependency types in TypeScript when replacing classes with pure functions. This approach applies to service boundaries, request handlers, and unit-tested functions, ensuring long-lived collaborators are explicitly injected per function rather than hidden inside class instances.

Replacing classes with dependency-injected functions improves testability by eliminating god objects and hidden couplings. The fn(args, deps) pattern forces explicit dependency declaration, allowing unit tests to easily provide mocks or stubs directly to the function without instantiating complex class hierarchies.

Yes, the fn(args, deps) pattern is ideal for service boundaries and request handlers. It supports codebases requiring per-call inputs and long-lived collaborators, allowing you to pass specific arguments alongside injected dependencies for clear, isolated, and testable service operations.