design-harden

Strengthen interfaces against edge cases, errors, internationalization issues, and real-world usage scenarios that break idealized designs.

Assess Hardening Needs

Identify weaknesses and edge cases:

1. Test with extreme inputs:

   • Very long text (names, descriptions, titles)
   • Very short text (empty, single character)
   • Special characters (emoji, RTL text, accents)
   • Large numbers (millions, billions)
   • Many items (1000+ list items, 50+ options)
   • No data (empty states)

2. Test error scenarios:

   • Network failures (offline, slow, timeout)
   • API errors (400, 401, 403, 404, 500)
   • Validation errors
   • Permission errors
   • Rate limiting
   • Concurrent operations

3. Test internationalization:

   • Long translations (German is often 30% longer than English)
   • RTL languages (Arabic, Hebrew)
   • Character sets (Chinese, Japanese, Korean, emoji)
   • Date/time formats
   • Number formats (1,000 vs 1.000)
   • Currency symbols

Designs that only work with perfect data are not production-ready. Harden against reality.

Reference file (read when assessing accessibility resilience):

• references/accessibility.md — WCAG 2.1 AA essentials, ARIA patterns, contrast requirements

Hardening Dimensions

Systematically improve resilience:

Text Overflow and Wrapping

Long text handling:

/* Single line with ellipsis */
.truncate {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* Multi-line with clamp */
.line-clamp {
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

/* Allow wrapping */
.wrap {
  word-wrap: break-word;
  overflow-wrap: break-word;
  hyphens: auto;
}

Flex/Grid overflow:

/* Prevent flex items from overflowing */
.flex-item {
  min-width: 0; /* Allow shrinking below content size */
  overflow: hidden;
}

/* Prevent grid items from overflowing */
.grid-item {
  min-width: 0;
  min-height: 0;
}

Responsive text sizing:

• Use clamp() for fluid typography
• Set minimum readable sizes (14px on mobile)
• Test text scaling (zoom to 200%)
• Ensure containers expand with text

Internationalization (i18n)

Text expansion:

• Add 30-40% space budget for translations
• Use flexbox/grid that adapts to content
• Test with longest language (usually German)
• Avoid fixed widths on text containers

// Bad: Assumes short English text
<button className="w-24">Submit</button>

// Good: Adapts to content
<button className="px-4 py-2">Submit</button>

RTL (Right-to-Left) support:

/* Use logical properties */
margin-inline-start: 1rem; /* Not margin-left */
padding-inline: 1rem; /* Not padding-left/right */
border-inline-end: 1px solid; /* Not border-right */

/* Or use dir attribute */
[dir="rtl"] .arrow { transform: scaleX(-1); }

Character set support:

• Use UTF-8 encoding everywhere
• Test with CJK characters
• Test with emoji (they can be 2-4 bytes)
• Handle different scripts (Latin, Cyrillic, Arabic)

Date/Time formatting:

// Use Intl API for proper formatting
new Intl.DateTimeFormat('en-US').format(date);
new Intl.DateTimeFormat('de-DE').format(date);

new Intl.NumberFormat('en-US', {
  style: 'currency',
  currency: 'USD'
}).format(1234.56);

Pluralization:

// Bad: Assumes English pluralization
`${count} item${count !== 1 ? 's' : ''}`

// Good: Use proper i18n library
t('items', { count }) // Handles complex plural rules

Error Handling

Network errors:

• Show clear error messages
• Provide retry button
• Explain what happened
• Offer offline mode if applicable
• Handle timeout scenarios

{error && (
  <ErrorMessage>
    <p>Failed to load data. {error.message}</p>
    <button onClick={retry}>Try again</button>
  </ErrorMessage>
)}

Form validation errors:

• Inline errors near fields
• Clear, specific messages
• Suggest corrections
• Do not block submission unnecessarily
• Preserve user input on error

API errors:

• 400: Show validation errors
• 401: Redirect to login
• 403: Show permission error
• 404: Show not found state
• 429: Show rate limit message
• 500: Show generic error, offer support

Graceful degradation:

• Core functionality works without JavaScript
• Images have alt text
• Progressive enhancement
• Fallbacks for unsupported features

Edge Cases and Boundary Conditions

Empty states: No items, no search results, no data. Provide clear next action.

Loading states: Initial load, pagination, refresh. Show what is loading and time estimates for long operations.

Large datasets: Pagination or virtual scrolling. Search/filter capabilities. Do not load all 10,000 items at once.

Concurrent operations: Prevent double-submission (disable button while loading). Handle race conditions. Optimistic updates with rollback.

Permission states: No permission to view/edit. Read-only mode. Clear explanation of why.

Browser compatibility: Polyfills for modern features. Fallbacks for unsupported CSS. Feature detection, not browser detection.

Input Validation and Sanitization

Client-side validation: Required fields, format validation, length limits, pattern matching, custom rules.

Server-side validation (always): Never trust client-side only. Validate and sanitize all inputs. Protect against injection. Rate limiting.

<input
  type="text"
  maxlength="100"
  pattern="[A-Za-z0-9]+"
  required
  aria-describedby="username-hint"
/>
<small id="username-hint">
  Letters and numbers only, up to 100 characters
</small>

Accessibility Resilience

Keyboard navigation: All functionality accessible via keyboard. Logical tab order. Focus management in modals. Skip links.

Screen reader support: Proper ARIA labels. Announce dynamic changes (live regions). Descriptive alt text. Semantic HTML.

Motion sensitivity:

@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

High contrast mode: Test in Windows high contrast mode. Do not rely only on color. Provide alternative visual cues.

Performance Resilience

Slow connections: Progressive image loading, skeleton screens, optimistic UI, offline support.

Memory leaks: Clean up event listeners, cancel subscriptions, clear timers, abort pending requests on unmount.

Throttling and debouncing:

const debouncedSearch = debounce(handleSearch, 300);
const throttledScroll = throttle(handleScroll, 100);

Testing Strategies

Manual testing: Test with extreme data, different languages, offline, slow connection (throttle to 3G), screen reader, keyboard-only, old browsers.

Automated testing: Unit tests for edge cases, integration tests for error scenarios, E2E for critical paths, visual regression, accessibility tests (axe, WAVE).

Verify Hardening

Test thoroughly with edge cases:

• Long text: Names with 100+ characters
• Emoji: Emoji in all text fields
• RTL: Arabic or Hebrew
• CJK: Chinese/Japanese/Korean
• Network issues: Disable internet, throttle connection
• Large datasets: 1000+ items
• Concurrent actions: Click submit 10 times rapidly
• Errors: Force API errors, test all error states
• Empty: Remove all data, test empty states

NEVER:

• Assume perfect input
• Ignore internationalization
• Leave error messages generic (“Error occurred”)
• Forget offline scenarios
• Trust client-side validation alone
• Use fixed widths for text
• Assume English-length text
• Block entire interface when one component errors