codex: Skill for Claude Code

React UI Patterns

Core Principles

1. Never show stale UI - Loading spinners only when actually loading
2. Always surface errors - Users must know when something fails
3. Optimistic updates - Make the UI feel instant
4. Progressive disclosure - Show content as it becomes available
5. Graceful degradation - Partial data is better than no data

Loading State Patterns

The Golden Rule

Show loading indicator ONLY when there's no data to display.

// CORRECT - Only show loading when no data exists
const { data, loading, error, refetch } = useGetItemsQuery();

if (error) return <ErrorState error={error} onRetry={refetch} />;
if (loading && !data) return <LoadingState />;
if (!data?.items.length) return <EmptyState />;

return <ItemList items={data.items} />;

// WRONG - Shows spinner even when we have cached data
if (loading) return <LoadingState />; // Flashes on refetch!

Loading State Decision Tree

Is there an error?
  → Yes: Show error state with retry option
  → No: Continue

Is it loading AND we have no data?
  → Yes: Show loading indicator (spinner/skeleton)
  → No: Continue

Do we have data?
  → Yes, with items: Show the data
  → Yes, but empty: Show empty state
  → No: Show loading (fallback)

Skeleton vs Spinner

Use Skeleton When	Use Spinner When
Known content shape	Unknown content shape
List/card layouts	Modal actions
Initial page load	Button submissions
Content placeholders	Inline operations

Error Handling Patterns

The Error Handling Hierarchy

1. Inline error (field-level) → Form validation errors
2. Toast notification → Recoverable errors, user can retry
3. Error banner → Page-level errors, data still partially usable
4. Full error screen → Unrecoverable, needs user action

Always Show Errors

CRITICAL: Never swallow errors silently.

// CORRECT - Error always surfaced to user
const [createItem, { loading }] = useCreateItemMutation({
  onCompleted: () => {
    toast.success({ title: 'Item created' });
  },
  onError: (error) => {
    console.error('createItem failed:', error);
    toast.error({ title: 'Failed to create item' });
  },
});

// WRONG - Error silently caught, user has no idea
const [createItem] = useCreateItemMutation({
  onError: (error) => {
    console.error(error); // User sees nothing!
  },
});