Conas a dhéanann tú staid a choinneáil seasmhach agus a uachta?

Question

Accepted Answer

Ciallaíonn **staid a choinneáil seasmhach** go sábhálann tú go stóras (localStorage, IndexedDB, backend) ionas go mairfidh sé athlóduithe leathanaigh nó seisiúin; ciallaíonn **uachtar** go lódálann tú ar ais isteach san aip ar thús oibrithe. Coitianta do bhascaí, comharthaí fíordheimhnithe, sainroghanna úsáideora, agus foirmeacha drafta.

## Coinneáil seasmhach agus uachtar bunúsach le localStorage

```jsx
function useCart() {
  // HYDRATE: initialize from storage (lazy initializer runs once)
  const [cart, setCart] = useState(() => {
    try {
      const saved = localStorage.getItem("cart");
      return saved ? JSON.parse(saved) : [];      // parse stored JSON
    } catch {
      return [];                                   // guard against corrupt data
    }
  });

// PERSIST: write to storage whenever it changes
  useEffect(() => {
    localStorage.setItem("cart", JSON.stringify(cart));
  }, [cart]);

return [cart, setCart];
}
```

An dá leath: a léamh agus a pharsáil ar thús (uachtar), agus a serialization agus a scríobh ar athrú (coinneáil seasmhach).

## Tacaíocht leabharlainne

```js
// Zustand persist middleware — automatic persist + hydrate
const useStore = create(persist((set) => ({ ... }), { name: "app-store" }));

// redux-persist for Redux; both handle serialization + rehydration
```

## Stóras a roghnú

```text
localStorage  → simple, synchronous, ~5–10MB, strings only (JSON) — preferences, small state
sessionStorage→ like localStorage but cleared when the tab closes
IndexedDB     → large/structured data, async — offline apps, big caches
Cookies       → sent to server; for auth (httpOnly for security)
Backend       → cross-device sync, source of truth for important data
```

## Na rabhadh thábhachtacha

```text
⚠️ SSR mismatch: localStorage doesn't exist on the server → guard with typeof window,
   and beware hydration mismatches between server-rendered and client state.
⚠️ Versioning/migration: stored shape may differ from new code → version it and migrate.
⚠️ Don't persist sensitive data (tokens) in localStorage (XSS-readable) — prefer httpOnly cookies.
⚠️ Don't persist server state you can refetch (let React Query handle caching).
⚠️ Validate/guard on hydrate — stored data can be stale or corrupt.
```

## Cén fáth a bhfuil sé tábhachtach

Tuigeann cobhsaíocht UX fíorluach — maireann bascaí athlóduithe, ní cailltear sainroghanna agus drafta, agus fanann úsáideoirí logáilte isteach.

Ach tugann cur i bhfeidhm naïve isteach fadhbanna fúarchúiseacha agus tubaisteach: neamhréireanna hidreatú SSR, sonraí sean-aosta nó truaillithe, briseadh aistrithe scéim, agus **rioscaí slándála** (coinneáil seasmhach comharthaí in stóras inléite XSS).

A bheith ar eolas faoin phatrún persist/hydrate, an stóras ceart a roghnú don sonraí, agus an rabhaidh a ghealladh (cosaint SSR, an scéim a leagan amach, gan rúnda a stóráil go neamhchosanta, gan staid an fhreastalaí a choinneáil seasmhach ar féidir a refetch) is ea an rud a dhéanann cobhsaíocht dhúbhailte ina ionad gur foinse de bhuganna deacra-a-dhiagnóisigh.