Spread and Rest

Short explanation

The spread operator (...) expands iterable values while rest parameters collect function arguments or remaining array elements.

Syntax example

const arr = [1, 2, 3];
const arr2 = [...arr, 4];

function sum(...nums) {
  return nums.reduce((a, b) => a + b, 0);
}

How JS handles it internally

Spread creates shallow copies for arrays and handles iterable unpacking. Rest parameters collect arguments into an array at call time.

FAQ

Q: Does spread perform deep cloning?

A: No — spread does a shallow copy. For deep cloning use structuredClone or a library.