Apa iku type assertion lan kapan iku mbiyayani?

Question

Accepted Answer

A **type assertion** ngandhani compiler "pitakon marang aku, nilai iki tegese X" nganggo `as`. Iku njaluk **ora ana runtime conversion utawa checking** — mung bab carane compiler ngrewangi nilai.

```ts
const el = document.getElementById("app") as HTMLInputElement;
el.value = "hi"; // compiler now allows .value (it assumed HTMLInputElement)

const data = JSON.parse(str) as User; // assert the parsed shape
```

## Kenapa iku mbiyayani

Sesarengan overrides compiler nyang — yen salah, sampeyan entuk runtime crash tanpa rembugan:

```ts
const x = "hello" as unknown as number; // double assertion — compiler stops complaining
x.toFixed(2); // 💥 runtime error: x.toFixed is not a function
```

Asserting ora nggawe nilai iku jenis kasebut; mung suda checker. Sampeyan wis njupuk tanggung jawab kanggo benar saka compiler.

## Pilihan sing luwih aman

```ts
// 1. type guard — actually verify at runtime
if (typeof input === "string") { /* input is string, proven */ }

// 2. validation library (zod) for external data
const user = UserSchema.parse(data); // throws if shape is wrong
```

## `as const` beda

```ts
const point = { x: 1 } as const; // not a risky cast — narrows to literal/readonly
```

## Kenapa iku penting

Assertions kadhang butuh (DOM APIs, narrowing `unknown` sing wis dicek), nanging saben siji iku papan compiler ora bisa nglindhungi sampeyan.

Nerangno type guards utawa schema validation kanggo data sing ora dipercaya, lan gawe saben `as` minangka cilik, disengaja "aku ngerti luwih" sing kudu sampeyan yakin ngenani.

Kenapa iku mbiyayani

Pilihan sing luwih aman

as const beda

Kenapa iku penting

`as const` beda