frontend-a11y

使い方

インストールコマンドをコピーし、自分の環境へ導入する前にソースを確認します。
必要なツール、認証情報、対応環境を原文で確認します。
入力と成果物を指定し、出力を資料と照合します。

npx skills add https://github.com/affaan-m/ecc --skill frontend-a11y

開始前の確認

導入にはモデル契約、API枠、ファイルへのアクセス許可は含まれません。
スター数や導入数は活動の指標であり、独立した品質・安全性試験ではありません。

リポジトリの原文

見出し、例、コード、表、リンク、参照画像を含む原文を表示しています。

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` 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-foundations and motion-patterns: animation patterns with accessibility considerations

使い方

開始前の確認

Frontend Accessibility Patterns

When to Activate

Form Accessibility

Label Connection

Required Fields

Error Messages

Complete Accessible Form

Semantic HTML

ARIA Attributes

aria-label vs aria-labelledby

aria-describedby

aria-live for Dynamic Content

aria-expanded and aria-controls

Keyboard Navigation

Custom Dropdown

Focus Management

Modal Focus Restoration

Images and Icons

Reduced Motion

Anti-Patterns

Checklist

Related Skills

タスクに関連する項目

関連する Skills

scientific-thinking-literature-review

docker-patterns

agentic-engineering

backend-patterns

frontend-a11y

使い方

開始前の確認

Frontend Accessibility Patterns

When to Activate

Form Accessibility

Label Connection

Required Fields

Error Messages

Complete Accessible Form

Semantic HTML

ARIA Attributes

aria-label vs aria-labelledby

aria-describedby

aria-live for Dynamic Content

aria-expanded and aria-controls

Keyboard Navigation

Custom Dropdown

Focus Management

Modal Focus Restoration

Images and Icons

Reduced Motion

Anti-Patterns

Checklist

Related Skills

タスクに関連する項目

backend-patterns

docker-patterns

python-patterns

rust-patterns

関連する Skills

scientific-thinking-literature-review

docker-patterns

agentic-engineering

backend-patterns