WORK STORY / 04
Split large monolithic components into modules with responsibility boundaries
Context
As features accumulated rapidly, some large components simultaneously handled presentation, data fetching, state control, and workflow logic. When AI or engineers kept adding features to the same file, a single change easily crossed multiple responsibilities, made testing difficult, and prevented code review from quickly identifying the true impact scope.
My Decision & Action
My goal was not merely to make files smaller, but to redefine responsibility and dependency boundaries. I separated UI, workflow coordination, data services, and pure logic into independent modules, and used Module Layering to restrict dependency direction. Tests moved with their responsibilities, using co-located tests to verify each module’s behavior instead of testing only the combined result from outside a giant component.
Outcome
Responsibilities formerly concentrated in one component were separated into modules that could be understood, modified, and verified independently. Feature changes could first be located in the responsible layer, while test boundaries aligned with code boundaries, reducing the risk that one requirement change would touch an entire feature chain.
Reflection
The real problem with a large component is not its line count, but too many responsibilities sharing the same change boundary. Good modularization does not simply fragment code; it makes every change able to answer clearly which responsibility is changing and what should remain unaffected.