Mene ne maɓugi optional (?) da readonly modifiers?

Question

IT Interview Practice · Accepted Answer

Waɗannan ƙaramin aiki suna sarrafa ko fage dole ne a ne da ko za a iya **sake damowa**.

## Optional (`?`)

```ts
interface User {
  name: string;
  email?: string; // optional — may be absent
}

const a: User = { name: "Ann" };               // ✅ email omitted
const b: User = { name: "Bo", email: "b@x" };  // ✅ included

function f(u: User) {
  u.email.length;   // ❌ Error: email is possibly 'undefined'
  u.email?.length;  // ✅ optional chaining handles the maybe-undefined
}
```

Fage ta daɗe yana da nau'i `T | undefined`, don haka mai juyawa zai damje ka sarrafa halin rashin jiya — sannan kawar da "cannot read property of undefined" caini.

## readonly

```ts
interface Point { readonly x: number; readonly y: number; }
const p: Point = { x: 1, y: 2 };
p.x = 5; // ❌ Error: cannot assign to readonly property

// arrays too
const nums: readonly number[] = [1, 2, 3];
nums.push(4); // ❌ push doesn't exist on readonly array
```

`readonly` shine lokaci-juyawa kawai (babu karfafa lokacin guida), amma yana bayyana da karfafa rashin sauyi a tsarin nau'i, da kama juyawa ta rashin sanin.

## Combined and at scale

```ts
interface Config { readonly id: string; tags?: readonly string[]; }
type Frozen = Readonly<User>; // utility type makes ALL props readonly
```

## Me ya sa yana da mahimmanci

`?` yana samar da bayani na gaske ta daɗe da karfafa sarrafa null; `readonly` yana bayyana da karfafa rashin sauyi (kyau ne ga ci gida, props, da kawar da sauyi na jiya ba sanin).

Duka biyu suna damje karfafa daidaita juyawa.

Optional (?)

readonly

Combined and at scale

Me ya sa yana da mahimmanci

Tambayoyi masu alaƙa

Optional (`?`)