@skmtc/gen-msw

An operation generator that demonstrates the shared-aggregate pattern: one Projection per operation contributes a route, and all routes converge into a single routesList Projection per file.

Source

skmtc-generators/gen-msw/src/

What it generates

Per operation, a MockRoute:

const getUserRoute = http.get('/users/:id', () => HttpResponse.json({ ... }))

Plus a shared aggregator MockRoutesList in the same file:

export const toRoutesList = (deps: { ... }) => [
  getUserRoute,
  createUserRoute,
  // ... all per-operation routes
]

The toRoutesList factory accepts dependencies (typically your mock data store) and returns the array MSW expects.

Key decisions

• Shared aggregate via findDefinition + defineAndRegister. The entry checks whether a toRoutesList already exists in the target file (findDefinition({ name, exportPath })). If yes, append the new route to its existing instance. If no, create one with defineAndRegister and append. This is the canonical pattern for "one Projection collects contributions from many."
• Factory-of-routes, not a const array. The aggregator produces a function so consumers can inject deps. This sidesteps the "module-level array of handlers needs a data store but data stores are created later" timing problem.
• No filtering via isSupported. All operations get a mock — GETs, POSTs, DELETEs, etc.

What to learn from it

• The shared-aggregate pattern. When you want one "index" file that lists all per-operation outputs, this is the template. Variants: gen-express and gen-supabase-hono use the same pattern with tiny-invariant-based assertions.
• findDefinition for idempotent aggregator creation. Looking up by (name, exportPath) lets multiple transform() calls converge on the same accumulator without races.
• Returning a factory. When generated output needs runtime dependencies, produce a function not a const. The consumer wires the deps at boot time.

Common customizations when cloned

• Swap MSW for a different mock library (e.g., Nock, Pollyjs).
• Change the response-shape generator (the stock produces HttpResponse.json({...}) from an example or a synthesized object; you may want to delegate to a fixture system).
• Customize the path-parameter substitution (/users/:id conversions are stock OAS-to-Express style; some routers use {id} instead).
• Change the aggregator's shape (return a Map, or a record by operationId, instead of an array).

See also

• API: GenerateContext — findDefinition / defineAndRegister
• gen-express — same shared-aggregate pattern, different aggregator shape
• Cross-generator coordination concept
• Projections and Snippets concept