Exercises and Phase Exit Practice Next.js independently, debug realistic failures, pass the architecture oral exam, and verify readiness for NestJS.
Exercises, Architecture Checks and Phase Exit The phase is complete only when you can reproduce the ideas without following every line. These exercises move from guided repetition toward independent engineering decisions.
Level 1 - Follow • Create the /projects and /settings routes from memory. • Add primary navigation in the root layout using Link. • Create one CSS Module and apply it to a project card. • Run dev, lint and build from the workspace root using a filter.
Level 2 - Modify • Add an /about route without changing the root layout API. • Add a descriptive empty state to /projects when the sample array is empty. • Improve visible keyboard focus for navigation links. • Add metadata appropriate for the application.
Level 3 - Implement Create a small ProjectStatusFilter Client Component that switches between All, Active and Planning for static sample projects. Keep the page as a Server Component if possible. Explain what data had to move into the client island and why.
Level 4 - Engineer Design a route structure for the future TaskFlow product without implementing backend data. Include dashboard, projects, a future project-detail route, and settings. Decide where a dashboard layout would live, which sections should share navigation, and where you would avoid route groups until the need is real.
Debugging scenarios Scenario Your diagnosis should start with
useState error in page.tsx Server/Client boundary; isolate interactive component
/projects is 404 Filesystem route structure and page.tsx location
pnpm --filter web says no package matched Check apps/web package name and workspace membershipWorks in dev, fails build Read build/type error; do not assume Fast Refresh proved correctness
Secret appears in browser bundle Treat as exposure; remove public prefix and redesign ownership
Architecture oral exam • Why can Next.js be called full-stack while this course still uses NestJS? • What is the difference between a route layout and a reusable UI component? • Why are Server Components the default? • What capabilities force a Client Component? • Why is use client at the root layout usually a poor first fix? • Why is NEXT_PUBLIC_ a security boundary?
• Why do we build with static data before inventing an API that does not exist yet?
Expected answers - concise • Next.js vs NestJS: Next.js has server capabilities, but TaskFlow centralizes authoritative domain rules in NestJS so there is one business API. • Layout vs component: a layout participates in the route tree and persists around descendant routes; a component is reusable UI independent of route semantics. • Server default: non-interactive UI can render without shipping component JavaScript to the browser and can use server capabilities. • Client requirement: browser event handlers, client hooks, browser APIs, or client-only libraries. • NEXT_PUBLIC_: it declares that a value may be included in browser-visible code; therefore secrets never belong there.
Phase exit checklist • I can recreate apps/web inside a pnpm monorepo without nesting Git or lockfiles. • I understand App Router pages, layouts and route segments. • I can explain Server versus Client Components using capabilities and network boundary. • I can build internal navigation with Link. • I understand loading, error and not-found as distinct UI states. • I can style with global CSS and CSS Modules without mixing responsibilities. • I understand public versus server-only environment variables. • I can diagnose common Next.js errors using terminal and browser evidence. • I can produce a successful production build.
What changed in the architecture BEFORE PHASE 03
taskflow repository (no application runtime)
Browser ^ | Next.js App Router | apps/web | TaskFlow monorepo
No backend yet. No database yet.
Next phase preview Phase 04 introduces a second independent runtime: NestJS with Fastify in apps/api. That phase will deliberately keep the two applications separate. Only Phase 06 will connect them over HTTP, so the learner can understand each side before crossing the network boundary.
Next.js is useful only when you can explain what runs on the server, what crosses into the browser, and which route owns a user-visible state.
Restate the goal of “Exercises and Phase Exit” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: route → Server Component → client boundary → request/data source → rendered UI. 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: A navigable TaskFlow web shell with route groups/layouts, server-first composition, selective client interactivity, and verified environment handling.. 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.
// app/tasks/page.tsx
import { TaskList } from "./task-list";
export default async function TasksPage() {
const tasks = await loadTasks();
return <TaskList initialTasks={tasks} />;
}Do 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.
Locate the first browser-only API or stateful hook and move the client boundary to the smallest component that needs it.
Verify route params, fetch location, cache behavior, and the exact server response before changing JSX.
Without copying the final source, create a second small scenario that applies “Exercises and Phase Exit” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Create nested routes and a shared layout, then predict which layouts persist across navigation.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Using effects for work that belongs in server rendering or a data layer
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.