Mene ne jefa da memoization a cikin sarrafa zaman fasali?

Question

Accepted Answer

A **selector** ne aiki da ke **karanta (cire) wani takamaiman fasali daga zaman fasali**. **Memoization** yana ajiye sakamakon selector don cewa ya sake ƙidaya kaɗai lokacin da abubuwan shigarsa suka canza — mahimmi ne don karfi lokacin da jefa ke buɗe aiki masu tsada ko don guje wa sake tunanin gida.

## Jefa na gida — adakili shigowa zaman fasali

```js
// a selector knows HOW to pull a value out of the state shape
const selectUser = state => state.user;
const selectCartItems = state => state.cart.items;
const selectCartTotal = state =>
  state.cart.items.reduce((sum, i) => sum + i.price, 0); // derived
```

Jefa na tsakantawa ilimin katsewar zaman fasali — abubuwan ba da ajiye `selectCartTotal(state)` ba tare da sanin inda/yadda aka ajiye shi, don haka idan katsewar zaman fasali ta canja kuna sabunta jefa guda daya, ba abubuwan duka ba.

## Matsalar: jefa da aka cire suka sake ƙidaya akan kiran duka

```js
const selectExpensiveList = state =>
  state.items.filter(i => i.active).sort(compareFn); // runs EVERY time, even if items didn't change
```

Jefa wanda ke ƙirƙira sabon jeri/abubuwa yana da kaimawo **sabon bayani** kiran duka — wanda zai iya haifar da sake tunani ba a buƙata (React ya ga "sabon" ƙima) da kuma ɓarna ƙidaya.

## Wareshi: jefa da aka tunanta (Reselect)

```js
import { createSelector } from "reselect"; // or RTK's createSelector

const selectActiveSorted = createSelector(
  [state => state.items],                       // input selector(s)
  (items) => items.filter(i => i.active).sort(compareFn) // recompute ONLY if items changed
);
```

`createSelector` yana ajiye sakamakon kuma shine kaiwa da tsada ƙidaya kaɗai lokacin da abubuwan shigarsa (`state.items`) a gaske suka canza — in ba haka ba jiya bakin rana sakamakon **daidai na bayani**, kawar da ƙidaya kuma koma tunani ga gida.

## Daidaita jefa

```js
const selectTotal = createSelector(
  [selectActiveSorted, selectTaxRate],          // build on other selectors
  (items, rate) => items.reduce((s, i) => s + i.price, 0) * (1 + rate)
);
```

Jefa yana daidaitawa, gina cire da take dari daga sauƙa, kawaye-kawaye tunantuna gida.

## Me ya sa shi mahimmi

Jefa ya keɓe abubuwan daga katsewar zaman fasali (bata nasara don gudummawar tunani) kuma saida wuri guda inda za a bayyana fasali da aka cire.

Memoization ya sanya jefa da aka cire mai ƙarfin gida — kawar da sake ƙidaya mai tsada da mahali da mahali, kuma murtuke, yana da dawo bayani ɗaya don haka abubuwan da aka haɗa ba su sake tunani ba cikin ba buƙata ba.

A cikin abubuwan Redux/NgRx, jefa da aka tunanta (Reselect/`createSelector`) ne kayan aiki na muhimmi ga karfi da gidaje; rabin tunani da taji tashi sai ne `useMemo` da `computed` saannan.