Apa bedane antara var, let lan const?

Question

IT Interview Practice · Accepted Answer

Beda-beda ing telu cara: **scope**, **hoisting behavior**, lan **reassignment**.

```js
function demo() {
  if (true) {
    var a = 1;    // function-scoped — leaks out of the if-block
    let b = 2;    // block-scoped — only exists inside { }
    const c = 3;  // block-scoped, can't be reassigned
  }
  console.log(a); // 1  (var escaped the block)
  console.log(b); // ReferenceError (let stayed in the block)
}
```

## Perbedaan utama

- **`var`** iku **function-scoped**, hoisted lan initialized menyang `undefined`, lan bisa redeclared. Iki nyebabake leaks sing nggumunake — atiköne.
- **`let`** iku **block-scoped** (`{ }`), reassignable, lan manggon ing *temporal dead zone* nganti baris deklarasinipun (akses awal njaluk error).
- **`const`** iku block-scoped lan **ora bisa reassigned** — nanging cathet yen binding iku constant, *bukan* nilai-ipun:

```js
const user = { name: "Ann" };
user.name = "Bob"; // ✅ allowed — mutating the object, not reassigning
user = {};          // ❌ TypeError — can't rebind `user`
```

## Pranata umum

Pilih **`const`** kanthi default; ganti menyang **`let`** mung upama kudu reassign; **aja nggunakake `var`** ing kode anyar. Iki nggawe maksud cetha ("iki ora bakal owah") lan nyegah scope leaks lan hoisting confusion sing `var` dawa.

Perbedaan utama

Pranata umum

Pitakon sing gegandhengan