Menene mai amincewa da baka-null (!) kuma yaushe ya dace?

Question

Accepted Answer

Postfix `!` yana gaya wa mai haɗa "Na tabbata wannan darajar ba null ba ko undefined ba" — yana cire `null`/`undefined` daga nau'insa ba tare da wata ƙuntatacciyar lokaci ba.

```ts
function f(name?: string) {
  // name is string | undefined
  console.log(name!.toUpperCase()); // `!` asserts it's defined → string
}
```

Abi ne na lokacin hada kawai — kamar `as`, ba ya yi **kome** bada-jiyya na lokaci ba. Idan ka kuruji, ya faɗi:

```ts
const el = document.getElementById("app")!; // assert non-null
el.innerHTML = "hi"; // 💥 runtime error if #app doesn't actually exist
```

## Lokacin da aka iya sa'a

```ts
// 1. You've logically guaranteed it, but the compiler can't see it
if (map.has(key)) map.get(key)!.doThing(); // has() proves get() isn't undefined

// 2. Class fields initialized outside the constructor (DI, lifecycle hooks)
class C { value!: string; } // definite assignment assertion
```

## Gida babbar halayen amincewa

```ts
name?.toUpperCase();           // optional chaining — no crash, yields undefined
const x = name ?? "default";    // provide a fallback
if (name) name.toUpperCase();   // narrow with a real check
```

Duk ɗaya daga cikinsu yana shakatawa yanayin da ba a gane ba maimakon kirkirra shi.

## Menene ya sa haka ya zama mahimmaci

`!` aiki ne mai karﻓi: yana shiyar da marmarin karewa mai aminci mai haɗa cewa yake gwaje-gwaje.

Ya zama sha'awa (kana da ilimi mai samu-samu ba ya ɗa sanin haka), amma idan ka kai wa girma sosai sai ka sake buɗe daidai rashin aminci-kasa buttude-bugaje wanda `strictNullChecks` ya dakatar.

Bari a je `?.`, `??`, ko bayyananniyar gadi a nan gida; buga `!` kawai lokacin da za ka iya tabbataa ba-ɗakatar-marmarin da gaske.