From 8fb728d7eb48e0524b6fc46affae1dd1e0cd09ad Mon Sep 17 00:00:00 2001
From: HJ <143365392+hjkim0905@users.noreply.github.com>
Date: Tue, 26 May 2026 03:09:14 +0900
Subject: [PATCH] feat(skills): add frontend accessibility skill (#2048)

Adds the frontend-a11y skill for React and Next.js accessibility patterns. Pre-validated against current main with validate-skills and markdownlint.
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+---
+name: frontend-a11y
+description: >
+  Accessibility patterns for React and Next.js — semantic HTML, ARIA attributes,
+  form labeling, keyboard navigation, focus management, and screen reader support.
+  Use when building any interactive UI component or form.
+origin: community
+---
+
+# Frontend Accessibility Patterns
+
+Practical accessibility patterns for React and Next.js. Covers the issues most commonly flagged in code review: missing form labels, incorrect ARIA usage, non-semantic interactive elements, and broken keyboard navigation.
+
+## When to Activate
+
+- Building or reviewing form components (`<input>`, `<select>`, `<textarea>`)
+- Creating interactive elements (modals, dropdowns, tooltips, tabs)
+- Using `<div>` or `<span>` with `onClick`
+- Adding `aria-*` attributes to any element
+- Implementing keyboard navigation or focus management
+- Receiving accessibility feedback from code review tools (CodeRabbit, ESLint a11y)
+- Building components that must support screen readers
+
+## Form Accessibility
+
+Missing `htmlFor` / `id` pairing and disconnected error messages are the most common issues flagged in code review.
+
+### Label Connection
+
+```tsx
+// BAD: label has no connection to input — screen readers cannot associate them
+<label>Email</label>
+<input type="email" />
+
+// GOOD: htmlFor matches input id
+<label htmlFor="email">Email</label>
+<input id="email" type="email" />
+```
+
+### Required Fields
+
+```tsx
+// BAD: visual-only asterisk conveys nothing to screen readers
+<label htmlFor="email">Email *</label>
+<input id="email" type="email" />
+
+// GOOD: required enables native browser validation; aria-required signals it to screen readers
+<label htmlFor="email">
+  Email <span aria-hidden="true">*</span>
+</label>
+<input id="email" type="email" required aria-required="true" />
+```
+
+### Error Messages
+
+```tsx
+// BAD: error text exists visually but is not linked to the input
+<input id="email" type="email" />
+<span className="error">Invalid email address</span>
+
+// GOOD: aria-describedby connects input to its error message
+// aria-invalid signals the invalid state to screen readers
+<input
+  id="email"
+  type="email"
+  aria-describedby="email-error"
+  aria-invalid={!!error}
+/>
+{error && (
+  <span id="email-error" role="alert">
+    {error}
+  </span>
+)}
+```
+
+### Complete Accessible Form
+
+```tsx
+interface LoginFormProps {
+  onSubmit: (email: string, password: string) => void;
+}
+
+export function LoginForm({ onSubmit }: LoginFormProps) {
+  const [email, setEmail] = useState('');
+  const [password, setPassword] = useState('');
+  const [errors, setErrors] = useState<{ email?: string; password?: string }>({});
+
+  const handleSubmit = (e: React.FormEvent) => {
+    e.preventDefault();
+    const newErrors: typeof errors = {};
+    if (!email) newErrors.email = 'Email is required';
+    if (!password) newErrors.password = 'Password is required';
+    if (Object.keys(newErrors).length) {
+      setErrors(newErrors);
+      return;
+    }
+    onSubmit(email, password);
+  };
+
+  return (
+    <form onSubmit={handleSubmit} noValidate>
+      <div>
+        <label htmlFor="email">
+          Email <span aria-hidden="true">*</span>
+        </label>
+        <input
+          id="email"
+          type="email"
+          value={email}
+          onChange={e => setEmail(e.target.value)}
+          aria-required="true"
+          aria-describedby={errors.email ? 'email-error' : undefined}
+          aria-invalid={!!errors.email}
+          autoComplete="email"
+        />
+        {errors.email && (
+          <span id="email-error" role="alert">
+            {errors.email}
+          </span>
+        )}
+      </div>
+
+      <div>
+        <label htmlFor="password">
+          Password <span aria-hidden="true">*</span>
+        </label>
+        <input
+          id="password"
+          type="password"
+          value={password}
+          onChange={e => setPassword(e.target.value)}
+          aria-required="true"
+          aria-describedby={errors.password ? 'password-error' : undefined}
+          aria-invalid={!!errors.password}
+          autoComplete="current-password"
+        />
+        {errors.password && (
+          <span id="password-error" role="alert">
+            {errors.password}
+          </span>
+        )}
+      </div>
+
+      <button type="submit">Log in</button>
+    </form>
+  );
+}
+```
+
+## Semantic HTML
+
+Use the element that matches the intent. Screen readers and keyboard users depend on native semantics.
+
+```tsx
+// BAD: div has no role, no keyboard support, no accessible name
+<div onClick={handleClick}>Submit</div>
+
+// GOOD: button is focusable, activates on Enter/Space, announces as "button"
+<button type="button" onClick={handleClick}>Submit</button>
+```
+
+```tsx
+// BAD: non-semantic navigation
+<div onClick={() => navigate('/home')}>Home</div>
+
+// GOOD: anchor supports right-click, middle-click, and keyboard navigation
+<a href="/home">Home</a>
+```
+
+```tsx
+// BAD: heading hierarchy skipped (h1 to h4)
+<h1>Dashboard</h1>
+<h4>Recent Activity</h4>
+
+// GOOD: sequential heading levels
+<h1>Dashboard</h1>
+<h2>Recent Activity</h2>
+```
+
+## ARIA Attributes
+
+Use ARIA only when native HTML semantics are insufficient. Wrong ARIA is worse than no ARIA.
+
+### aria-label vs aria-labelledby
+
+```tsx
+// aria-label: inline string label — use when no visible label text exists
+<button aria-label="Close modal">
+  <XIcon />
+</button>
+
+// aria-labelledby: references another element's text — use when a visible label exists
+<section aria-labelledby="section-title">
+  <h2 id="section-title">Recent Orders</h2>
+  {/* content */}
+</section>
+```
+
+### aria-describedby
+
+```tsx
+// Provides supplementary description beyond the label
+<button
+  aria-describedby="delete-warning"
+  onClick={handleDelete}
+>
+  Delete account
+</button>
+<p id="delete-warning">This action cannot be undone.</p>
+```
+
+### aria-live for Dynamic Content
+
+```tsx
+// Use aria-live to announce content that updates without a page reload
+// polite: waits for user to finish current action before announcing
+// assertive: interrupts immediately — use only for urgent errors
+
+export function StatusMessage({ message, isError }: { message: string; isError?: boolean }) {
+  return (
+    <div role="status" aria-live={isError ? 'assertive' : 'polite'} aria-atomic="true">
+      {message}
+    </div>
+  );
+}
+```
+
+### aria-expanded and aria-controls
+
+```tsx
+export function Accordion({ title, children }: { title: string; children: React.ReactNode }) {
+  const [isOpen, setIsOpen] = useState(false);
+  const contentId = useId();
+
+  return (
+    <div>
+      <button aria-expanded={isOpen} aria-controls={contentId} onClick={() => setIsOpen(prev => !prev)}>
+        {title}
+      </button>
+      <div id={contentId} hidden={!isOpen}>
+        {children}
+      </div>
+    </div>
+  );
+}
+```
+
+## Keyboard Navigation
+
+Every interactive element must be reachable and operable by keyboard alone.
+
+### Custom Dropdown
+
+```tsx
+export function Dropdown({ options, onSelect }: { options: string[]; onSelect: (value: string) => void }) {
+  const [isOpen, setIsOpen] = useState(false);
+  const [activeIndex, setActiveIndex] = useState(0);
+  const listId = useId();
+
+  if (!options.length) return null;
+
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    switch (e.key) {
+      case 'ArrowDown':
+        e.preventDefault();
+        setActiveIndex(i => Math.min(i + 1, options.length - 1));
+        break;
+      case 'ArrowUp':
+        e.preventDefault();
+        setActiveIndex(i => Math.max(i - 1, 0));
+        break;
+      case 'Enter':
+      case ' ':
+        e.preventDefault();
+        if (isOpen) onSelect(options[activeIndex]);
+        setIsOpen(prev => !prev);
+        break;
+      case 'Escape':
+        setIsOpen(false);
+        break;
+    }
+  };
+
+  return (
+    <div
+      role="combobox"
+      aria-expanded={isOpen}
+      aria-haspopup="listbox"
+      aria-controls={listId}
+      tabIndex={0}
+      onKeyDown={handleKeyDown}
+      onClick={() => setIsOpen(prev => !prev)}
+    >
+      <span>{options[activeIndex]}</span>
+      {isOpen && (
+        <ul id={listId} role="listbox">
+          {options.map((option, index) => (
+            <li
+              key={option}
+              role="option"
+              aria-selected={index === activeIndex}
+              onClick={() => {
+                onSelect(option);
+                setIsOpen(false);
+              }}
+            >
+              {option}
+            </li>
+          ))}
+        </ul>
+      )}
+    </div>
+  );
+}
+```
+
+## Focus Management
+
+Focus must move logically when UI state changes — especially for modals and route transitions.
+
+### Modal Focus Restoration
+
+> This example covers initial focus and restoration. For a full focus trap (Tab/Shift+Tab cycling within the modal), use a library like [`focus-trap-react`](https://github.com/focus-trap/focus-trap-react) which handles edge cases like dynamic content and nested portals.
+
+```tsx
+export function Modal({ isOpen, onClose, title, children }: { isOpen: boolean; onClose: () => void; title: string; children: React.ReactNode }) {
+  const modalRef = useRef<HTMLDivElement>(null);
+  const previousFocusRef = useRef<HTMLElement | null>(null);
+
+  useEffect(() => {
+    if (isOpen) {
+      // Save currently focused element and move focus into modal
+      previousFocusRef.current = document.activeElement as HTMLElement;
+      modalRef.current?.focus();
+    } else {
+      // Restore focus to the element that opened the modal
+      previousFocusRef.current?.focus();
+    }
+  }, [isOpen]);
+
+  if (!isOpen) return null;
+
+  return (
+    <div ref={modalRef} role="dialog" aria-modal="true" aria-labelledby="modal-title" tabIndex={-1} onKeyDown={e => e.key === 'Escape' && onClose()}>
+      <h2 id="modal-title">{title}</h2>
+      {children}
+      <button onClick={onClose}>Close</button>
+    </div>
+  );
+}
+```
+
+## Images and Icons
+
+```tsx
+// BAD: decorative icon announced as unlabeled image
+<img src="/icon.svg" />
+
+// GOOD: decorative image hidden from screen readers
+<img src="/decoration.png" alt="" aria-hidden="true" />
+
+// GOOD: meaningful image with descriptive alt text
+<img src="/chart.png" alt="Monthly revenue increased 23% from January to March" />
+
+// GOOD: icon button with accessible label
+<button aria-label="Delete item">
+  <TrashIcon aria-hidden="true" />
+</button>
+```
+
+## Reduced Motion
+
+Respect users who have requested reduced motion in their OS settings.
+
+```tsx
+export function useReducedMotion(): boolean {
+  const [prefersReduced, setPrefersReduced] = useState(false);
+
+  useEffect(() => {
+    const mq = window.matchMedia('(prefers-reduced-motion: reduce)');
+    setPrefersReduced(mq.matches);
+    const handler = (e: MediaQueryListEvent) => setPrefersReduced(e.matches);
+    mq.addEventListener('change', handler);
+    return () => mq.removeEventListener('change', handler);
+  }, []);
+
+  return prefersReduced;
+}
+
+// Usage
+export function AnimatedCard({ children }: { children: React.ReactNode }) {
+  const reduceMotion = useReducedMotion();
+
+  return (
+    <div
+      style={{
+        transition: reduceMotion ? 'none' : 'transform 300ms ease'
+      }}
+    >
+      {children}
+    </div>
+  );
+}
+```
+
+## Anti-Patterns
+
+```tsx
+// BAD: onClick on non-interactive element with no keyboard support
+<div onClick={handleClick}>Click me</div>
+
+// BAD: aria-label on a div that has no role
+<div aria-label="Navigation">...</div>
+
+// BAD: placeholder used as a substitute for label
+<input placeholder="Enter your email" />
+
+// BAD: positive tabIndex creates unpredictable tab order
+<button tabIndex={3}>Submit</button>
+
+// BAD: aria-hidden on a focusable element — keyboard users get trapped
+<button aria-hidden="true">Open</button>
+
+// BAD: role="button" on div without keyboard handler
+<div role="button" onClick={handleClick}>Submit</div>
+// Missing: tabIndex={0}, onKeyDown for Enter/Space
+```
+
+## Checklist
+
+Before submitting any interactive component for review:
+
+- [ ] Every `<input>`, `<select>`, and `<textarea>` has a connected `<label>` via `htmlFor`/`id`
+- [ ] Error messages are linked with `aria-describedby` and marked `role="alert"`
+- [ ] No `onClick` on `<div>` or `<span>` without `role`, `tabIndex`, and `onKeyDown`
+- [ ] Icon-only buttons have `aria-label`
+- [ ] Decorative images use `alt=""` and `aria-hidden="true"`
+- [ ] Modals restore focus on close (for full focus trapping with Tab/Shift+Tab cycling, use a library like `focus-trap-react`)
+- [ ] Dynamic content updates use `aria-live`
+- [ ] `prefers-reduced-motion` is respected for animations
+
+## Related Skills
+
+- `frontend-patterns` — general React component and state patterns
+- `design-system` — design token and component consistency
+- `motion-ui` — animation patterns with accessibility considerations