Precise API Contracts

When designing or documenting API options and callbacks, ensure the contract is exact, unambiguous, and type-safe.

• Specify true behavior and defaults: If an option affects multiple behaviors, document what it does exactly (including defaults). Prefer the control mechanism that precisely matches intent (e.g., stop polling by returning false from refetchInterval, not by disabling the query if that impacts more than polling).
• Make TypeScript reflect reality: Export/extract the correct public types, and ensure required/optional fields match current behavior (e.g., don’t claim mutationKey is required if it isn’t). Use narrower option types for wrappers (so unsupported options are rejected by TS rather than silently ignored).
• Avoid concept/name collisions: If different parts of the API use the same term (like multiple “context” meanings), either rename one concept or clearly distinguish them in docs and examples (optionally via a more explicit name like “scope”).
• Document cross-runtime input constraints: For SSR/server-action boundaries, ensure inputs are serializable; don’t pass function references as queryFn where only serializable values are allowed—call functions so arguments are safe.

Example (control-flow precision):

useQuery({
  queryKey: ['job', jobId],
  queryFn: () => fetchJobStatus(jobId),
  refetchInterval: (query) => {
    if (query.state.data?.status === 'complete') return false
    return 2000
  },
})