Frontend Components

Frontend Components

Framework selection (one-line picker)

Deep comparison: react-patterns.md, vue-patterns.md, svelte-patterns.md, web-components.md.

Workflow: build a new component

1. Define props API — name, types, required vs optional, default values, controlled-vs-uncontrolled pattern (accept optional value + onChange).
2. Render markup — semantic HTML first, then styling.
3. Wire state/effects — local state for ephemeral UI; lift to parent for shared.
4. Add a11y — role, aria-*, keyboard handlers, focus management. Verify with axe DevTools.
5. Write tests — render, interaction, a11y snapshot.
6. Document — Storybook story per variant + states (default, loading, error, disabled).

Checkpoint after step 4: run npx @axe-core/cli http://localhost:6006/iframe?id=<story> — fail build if any violation. Checkpoint after step 5: branch coverage on the component file must be >= 80% (vitest run --coverage).

Reference template (React + Suspense + custom hook)

import { Suspense, use, useEffect, useId, useState } from "react";

function useDebounced<T>(value: T, ms = 300): T {
  const [v, setV] = useState(value);
  useEffect(() => { const t = setTimeout(() => setV(value), ms); return () => clearTimeout(t); }, [value, ms]);
  return v;
}

export function SearchBox({ value, onChange, resultsPromise }: {
  value: string; onChange: (s: string) => void; resultsPromise: Promise<string[]>;
}) {
  const id = useId();
  const debounced = useDebounced(value);
  return (
    <div role="search">
      <label htmlFor={id}>Search</label>
      <input id={id} value={value} => onChange(e.target.value)} aria-describedby={`${id}-hint`} />
      <Suspense fallback={<p>Loading…</p>}>
        <Results promise={resultsPromise} query={debounced} />
      </Suspense>
    </div>
  );
}
function Results({ promise }: { promise: Promise<string[]>; query: string }) {
  const items = use(promise);
  return <ul>{items.map((i) => <li key={i}>{i}</li>)}</ul>;
}

Vue SFC, Svelte 5 runes, and Lit equivalents (same controlled-input + debounce pattern) live in vue-patterns.md, svelte-patterns.md, and web-components.md.

Pre-merge gates

npx size-limit                         # fail if component adds >5kb gzipped
npx @axe-core/cli http://localhost:6006/iframe.html?id=<story>  # zero violations
vitest run --coverage                  # branch coverage ≥80% on the component file

Long lists (>100 rows): use react-window / vue-virtual-scroller / svelte-virtual-list. Code-split modal/admin features (React.lazy, defineAsyncComponent, dynamic import()).

Next Steps

• Component Library: docs, testing, versioning
• CSS Architecture: styling strategy
• Design System Creation: tokens + governance
• Accessibility Audit: WCAG 2.2 AA
• Motion Design: purposeful animation