carousel-next-previous.js

// Get the next or previous index in an array
// and loop around if you exede the bounds.

// Found this in a Ryan Florence Video. Kept coming back
// to it so though I'd put it somewhere easier to find.
// Video here: https://youtu.be/wXLf18DsV-I?t=769

const nextIndex = (currentIndex, length) => (
  (currentIndex + 1 + length) % length
);

const previousIndex = (currentIndex, length) => (
  (currentIndex - 1 + length) % length
);