Menene abubuwan keyof da typeof suke aiki a cikin halin nau'in?

Question

Accepted Answer

Waɗannan masu aiki guda biyu suna ba ka izin na samun nau'ina daga nau'ina da dabi'u da aka sadu - asali na shirye-shirye a matakin nau'i.

## keyof — haɗin union na maɓuɓɓukin nau'ina

```ts
interface User { id: number; name: string; }
type UserKey = keyof User; // "id" | "name"
```

## typeof — nau'in dabi'a

```ts
const config = { host: "localhost", port: 3000 };
type Config = typeof config; // { host: string; port: number }
```

`typeof` (a cikin matsayin nau'i) ya kamata dabi'ar da aka kimanta ta jiya, saboda ba za ka buɗe nau'in sosai ba.

## Haɗi: na zamanin property getter mai ciyawa

```ts
function getProp<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}
const user = { id: 1, name: "Ann" };
getProp(user, "name"); // returns string
getProp(user, "age");  // ❌ Error: "age" is not a key of user
```

Here `K extends keyof T` yana ɗaure `key` zuwa ainihin mafintoni, da `T[K]` (nau'in *indexed access*) yana bada bada jujjuyawar nau'in dabi'a na ke da kyau. Haɗa kewa zu zuwa kuɗin.

## Samun union daga object na const

```ts
const Roles = { Admin: "admin", User: "user" } as const;
type Role = typeof Roles[keyof typeof Roles]; // "admin" | "user"
```

## Dalilin da yake mahimmanci

`keyof` da `typeof` suna haɗa duniyar dabi'a da duniyar nau'i.

Su suna abubuwan saniya na haɗin property ta ƙarƙashin ta-faɗi, samun nau'ina daga bayani/duka (tushen gida daya), da saniyoyin gida don jakar da yaliwar nau'in.

Su ne hanya da za ka tashi daga tura jiya ɗaya-ɗaya na nau'ina bayyanannu.