Apa sing ditindakake dening modifier optional (?) lan readonly?

Question

Accepted Answer

Modifier properti iki ngontrol apa properti iku **kudu ana** lan apa bisa **diowahi-owahi".

## 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
}
```

Propertyti opsional nduweni tipe `T | undefined`, mula compiler maksa sampeyan ngopeni kasus sing ilang — nyegah bug "cannot read property of undefined".

## 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` mung kompilasi wae (ora ana paksaan runtime), nanging iku dokumentation lan paksaan immutability ing sistem tipe, ngenteni mutasi sing accidental.

## Combined lan at scale

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

## Apa sing penting

`?` ndhuwe model data sing bener-bener opsional lan maksa null-safety; `readonly` ngandharake lan paksaan immutability (apik banget kanggo config, props, lan nyegah mutasi state sing accidental).

Rorone nedahake pengecekan kabenaran menyang compiler.

Optional (?)

readonly

Combined lan at scale

Apa sing penting

Optional (`?`)