Unshift Implementation

let numbers = [1, 2, 3, 4, 5];
let firstElement = 68;

function unshiftFirstElement(arr, element) {
  arr.length = arr.length + 1;
  let modifiedArr = [];

  for (let i = 0; i < arr.length; i++) {
    let currentElement = arr[i];
    if (currentElement === arr[i]) {
      currentElement = arr[i - 1];
    }
    modifiedArr[modifiedArr.length] = currentElement;
  }
  modifiedArr[0] = element;
  return modifiedArr;
}

let result = unshiftFirstElement(numbers, firstElement);
console.log(result);