Calculate fibonacci sequence based on two given starting numbers and up to a specified number of entries.

Calculate Fibonacci Sequence

let fib_num = function (n0, n1, fib_idx) {
  let next_num;
  for (let i = 0; i <= fib_idx; i++) {
    next_num = n0 + n1;
    n0 = n1;
    n1 = next_num;
  }
  console.log(`fibonacci number is: ${next_num}.`);
  return next_num;
};