Найти последний элемент массива произвольной длины.

const arr1 = ['yellow', 'green', 'white', 'orange'];
 
    const arr2 = [664, 976, 300, 500, 1087, 552, 765, 1122, 448, 8765];
 
    const arr3 = ['Ivan', 'Maria', true, 771, false, 'Monkey', 111, ['Mother', 'Father'], true, 998, 'Lisa'];

const getLastElement = (arr) => arr.slice().pop();
//const getLastElement = (arr) => arr[arr.length - 1]
for (let arr of [arr1, arr2, arr3]) {
  console.log(`последний элемент: ${getLastElement(arr)}`);
}

let getLastElement=(arr) => arr.slice(-1);

const getLastElement = arr => arr[arr.length - 1];

const arr = [664, 976, 300, 500, 1087, 552, 765, 1122, 448, 8765];
const withSlice = arr => arr.slice(-1);
const withLength = arr => arr[arr.length - 1];
 
console.log('withSlice', bench(withSlice, 100000, arr));
console.log('withLength', bench(withLength, 100000, arr));
 
function bench(func, times, ...args) {
  const start = Date.now();
  for (let i = 0; i < times; i++) func(...args);
  return Date.now() - start;
}

const getLastElement = arr => arr.slice(-1)[0];

function getLastElement(arr) {
  return arr[arr.length-1];
}
 
const arr1 = ['yellow', 'green', 'white', 'orange'];
const arr2 = [664, 976, 300, 500, 1087, 552, 765, 1122, 448, 8765];
const arr3 = ['Ivan', 'Maria', true, 771, false, 'Monkey', 111, ['Mother', 'Father'], true, 998, 'Lisa'];
console.log(getLastElement(arr1));
console.log(getLastElement(arr2));
console.log(getLastElement(arr3));

const getLastElement = arr => arr.slice(-1)[0];