N-th power.js

This kata is from check py.checkio.org

You are given an array with positive numbers and a non-negative number N. You should find the N-th power of the element in the array with the index N. If N is outside of the array, then return -1. Don't forget that the first element has the index 0.

Let's look at a few examples:

array = [1, 2, 3, 4] and N = 2, then the result is 3^2 == 9;
array = [1, 2, 3] and N = 3, but N is outside of the array, so the result is -1.

const index = (array, n) => array[n] ** n || -1;

or

const index = (array, n) => array.length > n ? Math.pow(array[n], n) : -1;

or 

function index(array, n){
    //your code here
    return array[n] ** n || -1;
  }