Find the Array Concatenation Value

export function findTheArrayConcVal(nums: number[]): number {
  function concatenate(num1: number, num2: number) {
    return parseInt(`${num1}${num2}`, 10);
  }
 
  let answer = 0;
  let [start, end] = [0, nums.length - 1];
  while (start <= end) {
    answer += start === end ? nums[start] : concatenate(nums[start], nums[end]);
    start += 1;
    end -= 1;
  }
  return answer;
}