Barrierefreie React-Komponenten von Grund auf entwickeln

// ❌ Div pretending to be a button — inaccessible by default
function BadButton({ onClick, children }: { onClick: () => void; children: React.ReactNode }) {
  return (
    <div className="btn" onClick={onClick}>
      {children}
    </div>
  );
}
 
// ✅ Semantic button — accessible automatically
function GoodButton({ onClick, children, ...props }: React.ButtonHTMLAttributes<HTMLButtonElement>) {
  return (
    <button className="btn" onClick={onClick} {...props}>
      {children}
    </button>
  );
}

// Semantic structure matters for screen readers
function ArticleCard({ title, excerpt, date, href }: ArticleCardProps) {
  return (
    <article aria-labelledby={`title-${href}`}>
      <header>
        <time dateTime={date}>{formatDate(date)}</time>
        <h3 id={`title-${href}`}>
          <a href={href}>{title}</a>
        </h3>
      </header>
      <p>{excerpt}</p>
    </article>
  );
}

function Modal({ isOpen, onClose, title, children }: ModalProps) {
  const modalRef = useRef<HTMLDivElement>(null);
  const previousFocusRef = useRef<HTMLElement | null>(null);
 
  useEffect(() => {
    if (isOpen) {
      // Store the element that had focus before opening
      previousFocusRef.current = document.activeElement as HTMLElement;
 
      // Move focus into the modal
      modalRef.current?.focus();
 
      return () => {
        // Restore focus when modal closes
        previousFocusRef.current?.focus();
      };
    }
  }, [isOpen]);
 
  // Trap focus inside the modal
  function handleKeyDown(event: React.KeyboardEvent) {
    if (event.key === "Escape") {
      onClose();
      return;
    }
 
    if (event.key !== "Tab") return;
 
    const focusableElements = modalRef.current?.querySelectorAll<HTMLElement>(
      'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])'
    );
 
    if (!focusableElements?.length) return;
 
    const first = focusableElements[0];
    const last = focusableElements[focusableElements.length - 1];
 
    if (event.shiftKey && document.activeElement === first) {
      event.preventDefault();
      last.focus();
    } else if (!event.shiftKey && document.activeElement === last) {
      event.preventDefault();
      first.focus();
    }
  }
 
  if (!isOpen) return null;
 
  return (
    <div className="modal-overlay" onClick={onClose} role="presentation">
      <div
        ref={modalRef}
        role="dialog"
        aria-modal="true"
        aria-labelledby="modal-title"
        tabIndex={-1}
        onKeyDown={handleKeyDown}
        onClick={(e) => e.stopPropagation()}
      >
        <h2 id="modal-title">{title}</h2>
        {children}
        <button onClick={onClose}>Close</button>
      </div>
    </div>
  );
}

function Tabs({ tabs }: { tabs: Array<{ label: string; content: React.ReactNode }> }) {
  const [activeIndex, setActiveIndex] = useState(0);
  const tabRefs = useRef<(HTMLButtonElement | null)[]>([]);
 
  function handleKeyDown(event: React.KeyboardEvent, index: number) {
    let newIndex = index;
 
    switch (event.key) {
      case "ArrowRight":
        newIndex = (index + 1) % tabs.length;
        break;
      case "ArrowLeft":
        newIndex = (index - 1 + tabs.length) % tabs.length;
        break;
      case "Home":
        newIndex = 0;
        break;
      case "End":
        newIndex = tabs.length - 1;
        break;
      default:
        return;
    }
 
    event.preventDefault();
    setActiveIndex(newIndex);
    tabRefs.current[newIndex]?.focus();
  }
 
  return (
    <div>
      <div role="tablist" aria-label="Content tabs">
        {tabs.map((tab, index) => (
          <button
            key={index}
            ref={(el) => { tabRefs.current[index] = el; }}
            role="tab"
            id={`tab-${index}`}
            aria-selected={index === activeIndex}
            aria-controls={`panel-${index}`}
            tabIndex={index === activeIndex ? 0 : -1}
            onClick={() => setActiveIndex(index)}
            onKeyDown={(e) => handleKeyDown(e, index)}
          >
            {tab.label}
          </button>
        ))}
      </div>
      {tabs.map((tab, index) => (
        <div
          key={index}
          role="tabpanel"
          id={`panel-${index}`}
          aria-labelledby={`tab-${index}`}
          hidden={index !== activeIndex}
          tabIndex={0}
        >
          {tab.content}
        </div>
      ))}
    </div>
  );
}

function useAnnounce() {
  const [message, setMessage] = useState("");
 
  const announce = useCallback((text: string, priority: "polite" | "assertive" = "polite") => {
    // Clear first to re-trigger announcement for identical messages
    setMessage("");
    requestAnimationFrame(() => setMessage(text));
  }, []);
 
  const AnnouncerRegion = useMemo(
    () =>
      function Announcer() {
        return (
          <div
            role="status"
            aria-live="polite"
            aria-atomic="true"
            className="sr-only"
          >
            {message}
          </div>
        );
      },
    [message]
  );
 
  return { announce, AnnouncerRegion };
}
 
// Usage in a form
function SearchForm() {
  const { announce, AnnouncerRegion } = useAnnounce();
  const [results, setResults] = useState<SearchResult[]>([]);
 
  async function handleSearch(query: string) {
    const data = await fetchResults(query);
    setResults(data);
    announce(`${data.length} results found for "${query}"`);
  }
 
  return (
    <form role="search" onSubmit={(e) => {
      e.preventDefault();
      const query = new FormData(e.currentTarget).get("q") as string;
      handleSearch(query);
    }}>
      <label htmlFor="search-input">Search</label>
      <input id="search-input" name="q" type="search" />
      <button type="submit">Search</button>
      <AnnouncerRegion />
      <ul aria-label="Search results">
        {results.map((r) => (
          <li key={r.id}>{r.title}</li>
        ))}
      </ul>
    </form>
  );
}

// jest + testing-library accessibility assertions
import { render, screen } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
import { axe, toHaveNoViolations } from "jest-axe";
 
expect.extend(toHaveNoViolations);
 
describe("Tabs component", () => {
  it("has no accessibility violations", async () => {
    const { container } = render(
      <Tabs
        tabs={[
          { label: "First", content: <p>First panel</p> },
          { label: "Second", content: <p>Second panel</p> },
        ]}
      />
    );
    const results = await axe(container);
    expect(results).toHaveNoViolations();
  });
 
  it("supports keyboard navigation", async () => {
    const user = userEvent.setup();
    render(
      <Tabs
        tabs={[
          { label: "First", content: <p>First panel</p> },
          { label: "Second", content: <p>Second panel</p> },
        ]}
      />
    );
 
    const firstTab = screen.getByRole("tab", { name: "First" });
    await user.click(firstTab);
    expect(firstTab).toHaveFocus();
 
    await user.keyboard("{ArrowRight}");
    expect(screen.getByRole("tab", { name: "Second" })).toHaveFocus();
    expect(screen.getByRole("tab", { name: "Second" })).toHaveAttribute(
      "aria-selected",
      "true"
    );
  });
});