A JavaScript method that will keep looping around an array, forward -- positive, or backward -- negative, when provided a valid or "out of bounds" index value.

carousel-index.js

const array = ['rock', 'paper', 'scissors'];

function carouselIndex(idx, array) {
  const negMap = { 1: 2, 2: 1, 0: 0 }; // go to sleep... make this dynamic to array size -- todo

  if (idx >= 0) {
    return array[idx % array.length];
  }
  
  return array[negMap[Math.abs(idx % 3)]];
}

// Tests
console.log( carouselIndex(0, array) ); // => "rock"
console.log( carouselIndex(2, array) ); // => "scissors"
console.log( carouselIndex(12, array) ); // => "rock"
console.log( carouselIndex(-1, array) ); // => "scissors"
console.log( carouselIndex(-8, array) ); // => "paper"