A simple function to help you access array values from the end. Source: https://stackoverflow.com/a/64296726

NegativeIndex.js

const nIndex = (array, nIndex) => array.slice(nIndex)[0];

// Example:
const arr = [1,2,3,5,7,9];
console.log(nIndex(arr, -2)); // output: 7
console.log(nIndex(arr, -4)); // output: 3