Code Review — UI / Frontend Layer

Focus on accessibility, performance, and correctness at the rendering boundary.

Accessibility (WCAG AA)

• Missing alt text on images — every <img> needs an alt attribute. Decorative images use alt="". Never alt="image" or alt="photo".
• Interactive element is not keyboard-accessible — a <div onClick> or <span onClick> is not focusable by default. Use <button> or add role/tabIndex and keyboard event handlers.
• Color contrast — text must meet 4.5:1 contrast ratio (3:1 for large text). Check with a contrast analyzer before approving color changes.
• Missing form labels — every <input> needs a visible <label> or aria-label. Placeholder text is not a substitute.
• Inaccessible error messages — form validation errors must be associated with the input (aria-describedby) and announced to screen readers.
• Focus management after state change — modals, dialogs, and popups must move focus to the new content on open and restore it on close.
• Missing ARIA role on custom widget — a custom dropdown, slider, or menu must declare its ARIA role and maintain ARIA state (aria-expanded, aria-selected, etc.).

State Management

• Server state stored in client state — data fetched from an API stored in useState/useReducer/Vuex instead of a server state cache (React Query, SWR, Apollo). Leads to stale reads and manual invalidation bugs.
• Derived state stored explicitly — const [fullName, setFullName] = useState(...) when fullName = firstName + lastName is derivable. Store the minimum, compute the rest.
• State updated without immutability — mutating a React/Vue state object directly (state.items.push(...)) instead of returning a new reference. Breaks change detection.
• Global state for local data — adding to a global store (Redux, Zustand, Pinia) something only one component uses. Use useState / component-local state first.
• Missing loading / error states — async data fetch with no handling of the pending or error case. The UI silently shows nothing or crashes.

Rendering & Performance

• Missing key on list items — rendering a list without a stable, unique key prop. React/Vue uses key for reconciliation; missing or array-index keys cause incorrect re-renders.
• Unnecessary re-renders — a component re-renders on every parent update because a prop (often an inline object or callback) is recreated each render. Stabilize with useMemo/useCallback/memo.
• Blocking the main thread — expensive computation in a render method or event handler without requestIdleCallback, a Web Worker, or useDeferredValue.
• Waterfall data fetching — child components that each fetch their own data serially. Hoist fetches to a parent or use parallel queries.
• Layout thrashing — reading and writing DOM properties (e.g., element.offsetHeight) in a loop causes repeated reflows. Batch reads before writes.

Bundle Size

• Unguarded heavy import — import * as moment from 'moment' (300 kB) when only one function is needed. Use a lighter alternative (date-fns) or a named import.
• Missing code splitting — a rarely-used heavy route imported eagerly. Use React.lazy / dynamic import() for route-level or feature-flag-gated code.
• Polyfill included unconditionally — polyfills for features that target browsers already support. Check browserslist config.
• Duplicate dependency — two packages that provide the same thing (e.g., lodash and lodash-es, or both axios and fetch wrappers). Pick one.

Hydration & SSR

• Hydration mismatch — rendering different content on the server vs. client (using window, Date.now(), or random values during SSR). Wrap in useEffect or a client-only boundary.
• Missing Suspense boundary — a lazy-loaded component or async data source with no <Suspense> fallback. Crashes or shows nothing during loading.
• Client-only APIs accessed in SSR — localStorage, document, window accessed outside a lifecycle hook or useEffect. Will throw during server rendering.

See Also

• .claude/skills/code-review/SKILL.md — general review checklist for all layers
• .claude/skills/react-best-practices/SKILL.md — React-specific patterns and hooks rules
• .claude/skills/accessibility/SKILL.md — detailed WCAG 2.2 accessibility guidance