Shift Implementation

let numbers = ["10", "20"];

function shiftFirstElement(arr) {
  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.length = modifiedArr.length - 1;
  return modifiedArr;
}

let result = shiftFirstElement(numbers);
console.log(result);
console.log(numbers[0]);