Apa iku iterators lan generators?

Question

Accepted Answer

An **iterator** adalah obyek dengan metode `next()` yang bali `{ value, done }`. Obyek iku **iterable** yen duwe metode `[Symbol.iterator]` — iku sing ndadekne `for...of` lan spread bisa gawé. A **generator** (`function*`) minangka cara sing mudah kanggo nggawé iterators sing bisa **pause lan resume** karo `yield`.

## Generators ngasilaken nilei kanthi malas

```js
function* idGenerator() {
  let id = 1;
  while (true) {     // infinite, but lazy — only computes on demand
    yield id++;      // pause here, return a value, resume on next()
  }
}
const gen = idGenerator();
gen.next().value; // 1
gen.next().value; // 2 — execution resumed where it paused
```

Gedhe ideé: eksekusi **stop** ing saben `yield` lan **mbalik maneh** ing `.next()` sesuk, njaga kaanan lokal antaré panggilan. Ora ana sing dihitung nganti sampeyan takon.

## Mengapa kemalasan iku penting

```js
// process a huge/infinite sequence without building it all in memory
function* take(iterable, n) {
  let i = 0;
  for (const x of iterable) {
    if (i++ >= n) return;
    yield x;
  }
}
[...take(idGenerator(), 3)]; // [1, 2, 3] — from an infinite generator
```

## Nggawé iterable khusus

```js
const range = {
  from: 1, to: 3,
  *[Symbol.iterator]() { for (let i = this.from; i <= this.to; i++) yield i; },
};
[...range]; // [1, 2, 3] — works with for...of and spread
```

## Mengapa iku penting

Generators ngidupake urutan malas/tanpa wates, iterasi khusus, lan streaming sing hemat memori.

Semono ugo dadi landasan perpustakaan async awal (co) lan ndasari iterasi async (`for await...of`).

Protokel iterator iku sing ngrungokne `for...of`, spread, lan destructuring ing arrays, Maps, Sets, lan strings.