Fullstack UX Designer

Professional UX expertise for Next.js/NestJS full-stack applications.

Extends: Generic UX Designer - Read base skill for design thinking process, research methods, interaction patterns, and critique framework.

Full-Stack UX Considerations

Server-Side Rendering UX

| Scenario | UX Pattern | | ----------------- | ------------------------------------------------ | | Initial page load | Hydration-safe skeleton screens | | Data fetching | Server components for static, client for dynamic | | Authentication | Protected routes with redirect UX | | Form submission | Progressive enhancement |

Hydration-Safe Patterns

// ✓ Avoid hydration mismatch
function Timestamp({ date }: { date: Date }) {
  const [formatted, setFormatted] = useState("");

  useEffect(() => {
    setFormatted(date.toLocaleString()); // Client-side only
  }, [date]);

  return <span>{formatted || "Loading..."}</span>;
}

API Loading & Error States

Loading State Hierarchy

| Duration | Pattern | Example | | ---------- | --------------- | ------------ | | < 100ms | No indicator | Button click | | 100ms - 1s | Subtle spinner | Form submit | | 1s - 5s | Skeleton screen | Page fetch | | > 5s | Progress bar | File upload |

Error State Design

API Error → Parse Error → User-Friendly Message → Recovery Action

| Error Type | User Message | Recovery | | ---------------- | ---------------------- | ----------------- | | 400 Validation | Show field errors | Fix and retry | | 401 Unauthorized | "Please log in" | Redirect to login | | 404 Not Found | "Item not found" | Navigate back | | 500 Server Error | "Something went wrong" | Retry button |

Optimistic UI Pattern

// Show immediate feedback, rollback on error
async function toggleLike(postId: string) {
  // 1. Update UI immediately
  setLiked(true);
  setLikeCount((c) => c + 1);

  try {
    // 2. Call API
    await api.like(postId);
  } catch {
    // 3. Rollback on failure
    setLiked(false);
    setLikeCount((c) => c - 1);
    showToast("Failed to like");
  }
}

When to Use Optimistic UI

| Action | Optimistic? | Why | | ------------- | ----------- | -------------------------- | | Like/favorite | Yes | Low risk, common action | | Add comment | Yes | Can show pending state | | Delete item | No | Destructive, needs confirm | | Payment | No | Critical, must verify | | Form submit | Maybe | Depends on complexity |

Form Submission UX

Client → Server Flow

User Input → Client Validation → Submit → Server Validation → Response
     ↓              ↓              ↓              ↓              ↓
  Feedback    Inline errors   Loading...   Field errors    Success/Error

Multi-Step Forms

// Show progress and allow back navigation
<FormStepper
  steps={["Details", "Payment", "Confirm"]}
  currentStep={step}
  onBack={() => setStep((s) => s - 1)}
/>

Authentication UX

Login Flow Patterns

| State | UX | | ------------- | ---------------------------- | | Loading auth | Full-page skeleton | | Not logged in | Show login form | | Logging in | Disable form, show spinner | | Success | Redirect with toast | | Error | Inline error, keep form data |

Protected Route Pattern

// Redirect unauthenticated users
if (!user && !loading) {
  return <Navigate to="/login" state={{ from: location }} />;
}

Real-Time Updates

| Pattern | Use Case | | --------- | ------------------------------------- | | Polling | Low-frequency updates (notifications) | | WebSocket | Chat, live collaboration | | SSE | One-way server updates |

Presence Indicators

Online status dots
"User is typing..." indicators
Collaborative cursors

Full-Stack Design Critique

| Aspect | Questions | | ---------------- | -------------------------------- | | Loading states | What shows during API calls? | | Error recovery | Can users recover from errors? | | Offline behavior | What happens without network? | | Auth transitions | Smooth login/logout experience? | | Data freshness | Is stale data clearly indicated? |

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