Apa iku spread lan rest operators?

Question

Accepted Answer

Loro-lorone nggunakake `...` nanging ing **arah sing jenenge**: spread **mbalekake** collection dadi item-item terpisah; rest **ngumpul-ngumpulake** item dadi siji array/object.

## Spread — balekake

```js
const a = [1, 2], b = [3, 4];
const merged = [...a, ...b];          // [1, 2, 3, 4]
const copy = [...a];                   // shallow copy
const obj = { ...user, active: true }; // copy object + override/add a field
Math.max(...[1, 5, 3]);                // 5 — spread array into arguments
```

## Rest — ngumpulake

```js
function sum(...nums) {     // gather all args into an array
  return nums.reduce((a, n) => a + n, 0);
}
sum(1, 2, 3);               // 6

const [first, ...others] = [10, 20, 30]; // first=10, others=[20, 30]
const { id, ...rest } = user;            // pull out id, keep the rest
```

## Detail sing penting: spread iku SHALLOW copy

```js
const original = { user: { name: "Ann" } };
const copy = { ...original };
copy.user.name = "Bob"; // ⚠️ also changes original.user.name — nested object is SHARED
```

Spread ngisor-isorane level paling ndhuwur; obyek sing ana ing njero isih dadi shared references. Kanggo state updates, biasane sampeyan mung ngganti level paling ndhuwur, sing apa-apane, nanging ewase wani kanggo struktur sing jero.

## Tumrap apa

Spread iku cara standar kanggo nggawe **immutable updates** (copy + ngganti) ing React/Redux, lan rest nggawe fungsi variadic lan destructuring "ngumpul-ngumpulake sisa" sing bersih.