3.5.9 Es 4

export function fibo(n) {
  if (n<1) return undefined;
  arr=fiboarray(n);
  return arr[n];
}

export function fibosomma(n) {
  if (n<1) return undefined;
  arr=fiboarray(n);
  let somma=0;
  for(let i in arr) { somma += arr[i]; }

  //Soluzione ES6: somma=arr.reduce((a, b) => a + b, 0);
  return somma;
}

export function fiboarray(n) {
  if (n<1) return undefined;
  let fib = [];
  fib[0] = 0;
  fib[1] = 1;
  for (let i = 2; i <= n; i++) {
    fib[i] = fib[i - 2] + fib[i - 1];
  }
  return fib;
}