Destructure

You can destructure an array just like you can an object.

const nums = [1, 2, 3];

function double([a, b, c]) {
  return [a * 2, b * 2, c * 2];
}

const [x, y, z] = double(nums);
console.log(x, y, z);
// 2 4 6

If you're only interested in the first element, you can destructure just that element, from the same code:

const [x] = double(nums);
console.log(x);
// 2

If you're unsure how many elements there are, you can use the rest operator ... to capture the rest of the elements into a new array:

const [x, ...theRestOfThem] = double(nums);
console.log(x);
// 2
console.log(theRestOfThem);
// [4, 6]

If you over-destructure, you'll get undefined:

const [x, y, z, a] = double(nums);
console.log(x, y, z, typeof a);
// 2 4 6 undefined

The variable created with ... is always an array; if there are no remaining elements, it will simply be an empty array []

const [x, y, z, ...a] = double(nums);
console.log(x, y, z, a);
// 2 4 6 []