length of linked list

length.js

function solution(A) {
  const len = A.length;
  if (len <= 1) {
    return len;
  }
  let K = 0;
  let size = 0;
  while (K != -1) {
    K = A[K];
    console.log("K: ", K);
    size++;
  }
  return size;
  // write your code in JavaScript (Node.js 8.9.4)
}
console.log("solution: ", solution([1, 5, -1, 4, 3, 2]));