typed-service-contracts

To handle errors as values in TypeScript, define a discriminated Result type within a Spec and implement a Handler that catches parsing or business logic failures and maps them into the Result. This ensures the Handler never throws exceptions, returning deterministic outputs.

The Spec and Handler pattern is an architecture standard that separates input parsing, business logic, and error handling. A Spec defines schemas and a Result type, while a Handler implements the contract and maps errors into the Result for deterministic behavior.

Enforce a strict contract by creating a Spec that defines explicit input, output, and error schemas alongside a capability interface. The Handler then implements this contract, ensuring side effects strictly follow the defined Result type boundaries.

Yes, the Spec and Handler pattern applies to CLIs, libraries, and complex business logic where inputs must be parsed. It treats each user request as a unit of work, making it suitable for various TypeScript application types.

The best way to structure deterministic error handling is using Design by Contract principles. Define a vertical slice architecture where a Spec outlines error schemas and the Handler maps failures into a discriminated Result type rather than throwing exceptions.

Avoid error-as-value patterns when your application relies on simple, linear logic where exception throwing is sufficient. This Spec and Handler architecture targets complex business boundaries requiring strict input parsing and deterministic Result mapping.