Loading, Empty, Error & Not-Found States Design explicit states for every route outcome
Phase 20 - Production Application UI Volume 06 - Professional Frontend
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Phase 20 turns the secure full-stack foundation into a coherent, accessible application interface without moving business authority into the browser.
A production page has more than a success state Every route that depends on network/data conditions needs deliberate loading, empty, error, unauthorized, forbidden, and not-found experiences. “Nothing rendered” is not an acceptable state.
Loading Work is in progress; preserve surrounding shell
Empty Request succeeded; no matching data
Error Request failed; recovery action if possible
Unauthorized Authentication required; usually redirect/sign-in
Next.js route state files tasks/ ■■■ page.tsx ■■■ loading.tsx ■■■ error.tsx // Client Component; gets reset() ■■■ not-found.tsx
Error boundary behavior Next.js `error.tsx` wraps a route segment in an error boundary and must be a Client Component. Its `reset()` callback can retry rendering the segment, making it appropriate for recoverable route failures.
A 200 response with zero matching tasks is a successful state. Give users context and a next step, such as clearing filters or creating a task.
Skeletons later, semantics now Phase 20 may use simple text/loading placeholders. Skeleton polish can be added when it mirrors the final layout. Avoid fake progress indicators that provide no information.
Loading Empty Error and NotFound States matters because it changes a real boundary in TaskFlow. The goal is to understand the inputs, owner, observable output, and failure modes before adding more abstraction.
Restate the goal of “Loading Empty Error and NotFound States” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: value → owner → lifetime → source of truth → consumer. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: TaskFlow responsive shell with navigation, workspace context, task screens, loading/empty/error states, and accessible interactions.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
API task rows -> TanStack Query
Search/filter URL -> URL/search params
Create form fields -> React Hook Form
Dialog open/closed -> local UI state
Authenticated user -> auth/session stateDo not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Return to the nearest observable boundary: input, network, process log, database, or rendered UI. Compare actual evidence with the predicted path.
Change one variable at a time and reproduce the original failure after the fix; otherwise you have correlation, not diagnosis.
Without copying the final source, create a second small scenario that applies “Loading Empty Error and NotFound States” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Exercise all non-happy states by forcing no data, slow data, error, and forbidden responses.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Global client component wrapping the whole app
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.