Fibonacci Algorithm

function fibRec(n) { return n <= 1 ? n : fibRec(n-1) + fibRec(n-2); }
function fibIter(n) {
  let a = 0, b = 1, temp;
  for(let i=2; i<=n; i++) { temp = a + b; a = b; b = temp; }
  return n ? b : a;
}
const memo = {0: 0, 1: 1};
function fibMemo(n) {
  if (memo[n] !== undefined) return memo[n];
  return memo[n] = fibMemo(n-1) + fibMemo(n-2);
}
const target = 15;