web-accessibility（网络可访问性）

Web Accessibility

Build interfaces that work for everyone. These are not optional enhancements — they are baseline quality.

Semantic HTML

Use the right element for the job. Never simulate interactive elements with <div>.

// BAD: div with click handler
<div onClick={handleClick} className="button">Submit</div>

// GOOD: semantic button
<button onClick={handleClick}>Submit</button>

// BAD: div as link
<div onClick={() => router.push('/about')}>About</div>

// GOOD: anchor/Link for navigation
<Link href="/about">About</Link>

Element Selection Guide

Keyboard Navigation

Every interactive element must be keyboard accessible.

Focus Management

/* NEVER remove focus indicators without replacement */
/* BAD */
*:focus { outline: none; }

/* GOOD: Visible focus only on keyboard navigation */
.interactive:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

/* Group focus for compound controls */
.input-group:focus-within {
  outline: 2px solid var(--color-accent);
}

Keyboard Event Handling

// Interactive custom elements need keyboard support
function CustomButton({ onClick, children }: { onClick: () => void; children: React.ReactNode }) {
  return (
    <div
      role="button"
      tabIndex={0}
      onClick={onClick}
      onKeyDown={(e) => {
        if (e.key === 'Enter' || e.key === ' ') {
          e.preventDefault();
          onClick();
        }
      }}
    >
      {children}
    </div>
  );
}
// Better: just use <button> and avoid all of the above

Skip Links

Provide skip navigation for keyboard users.

<a href="#main-content" className="sr-only focus:not-sr-only focus:absolute focus:top-4 focus:left-4 focus:z-50">
  Skip to main content
</a>

Headings used as scroll targets need offset for fixed headers:

[id] { scroll-margin-top: 5rem; }

ARIA Patterns

Icon Buttons

// Icon-only buttons MUST have aria-label
<button aria-label="Close dialog" onClick={onClose}>
  <XIcon aria-hidden="true" />
</button>

// Decorative icons are hidden from screen readers
<span aria-hidden="true">🔒</span> Secure connection

Live Regions

Announce dynamic content changes to screen readers.

// Toast notifications
<div role="status" aria-live="polite">
  {notification && <p>{notification.message}</p>}
</div>

// Error alerts
<div role="alert" aria-live="assertive">
  {error && <p>{error.message}</p>}
</div>

Loading States

<button disabled={isLoading} aria-busy={isLoading}>
  {isLoading ? 'Saving\u2026' : 'Save'}  {/* proper ellipsis character */}
</button>

// Skeleton screens
<div aria-busy="true" aria-label="Loading content">
  <Skeleton />
</div>

Forms

Labels

Every input must have an associated label.

// GOOD: Explicit association
<label htmlFor="email">Email</label>
<input id="email" type="email" autoComplete="email" />

// GOOD: Wrapping (clickable label, no htmlFor needed)
<label>
  Email
  <input type="email" autoComplete="email" />
</label>

// GOOD: Visually hidden but accessible
<label htmlFor="search" className="sr-only">Search</label>
<input id="search" type="search" placeholder="Search..." />

Input Types and Autocomplete

Use semantic input types to get the right mobile keyboard and browser behavior.

<input type="email" autoComplete="email" />
<input type="tel" autoComplete="tel" />
<input type="url" autoComplete="url" />
<input type="password" autoComplete="current-password" />
<input type="password" autoComplete="new-password" />

Validation and Errors

<div>
  <label htmlFor="email">Email</label>
  <input
    id="email"
    type="email"
    aria-invalid={!!errors.email}
    aria-describedby={errors.email ? 'email-error' : undefined}
  />
  {errors.email && (
    <p id="email-error" role="alert" className="text-red-600">
      {errors.email}
    </p>
  )}
</div>

Form Behavior Rules

• Never prevent paste on any input
• Disable spellcheck on emails and codes: spellCheck={false}
• Submit button stays enabled until request starts; show spinner during loading
• Focus first error on submit failure
• Checkboxes and radio buttons: single hit target, no dead zones between label and input

Images and Media

// Informative images: descriptive alt
<img src="chart.png" alt="Revenue grew 40% from Q1 to Q3 2025" />

// Decorative images: empty alt
<img src="divider.svg" alt="" />

// Prevent layout shift: always set dimensions
<img src="photo.jpg" width={800} height={600} alt="Team photo" />

// Below fold: lazy load
<img src="photo.jpg" loading="lazy" alt="..." />

// Critical: prioritize
<img src="hero.jpg" fetchPriority="high" alt="..." />

Touch and Mobile

Touch Targets

Minimum 44x44px for all interactive elements (WCAG 2.5.5).

.touch-target {
  min-height: 44px;
  min-width: 44px;
}

Safe Areas

Handle device notches and home indicators.

.full-bleed {
  padding-top: env(safe-area-inset-top);
  padding-bottom: env(safe-area-inset-bottom);
  padding-left: env(safe-area-inset-left);
  padding-right: env(safe-area-inset-right);
}

Touch Behavior

/* Prevent 300ms delay and highlight flash */
.interactive {
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
}

/* Prevent scroll chaining on modals */
.modal { overscroll-behavior: contain; }

Internationalization

// BAD: Hardcoded formats
const date = `${month}/${day}/${year}`;
const price = `$${amount.toFixed(2)}`;

// GOOD: Locale-aware formatting
const date = new Intl.DateTimeFormat(locale).format(new Date());
const price = new Intl.NumberFormat(locale, {
  style: 'currency',
  currency: 'USD',
}).format(amount);

// Detect language
const lang = request.headers.get('accept-language')?.split(',')[0] ?? 'en';

Performance for Accessibility

• Lists > 50 items: virtualize
• Critical fonts: <link rel="preload" as="font"> with font-display: swap
• Avoid layout reads during render (causes jank for screen reader users too)
• Uncontrolled inputs perform better than controlled for large forms

Checklist

Use this for review:

• All interactive elements are keyboard accessible
• Focus indicators are visible on :focus-visible
• Color contrast meets WCAG AA (4.5:1 body, 3:1 large text)
• Images have appropriate alt text
• Form inputs have labels
• Error messages are associated with inputs via aria-describedby
• Icon-only buttons have aria-label
• Dynamic content uses aria-live regions
• Touch targets are minimum 44x44px
• prefers-reduced-motion is respected
• No outline: none without replacement focus style
• Heading hierarchy is sequential (no skipped levels)