JS Bin // source http://jsbin.com/kawomaxiga

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

function memoizedFibSum(num) {
  if (!this.cache) {
    this.cache = {};
  }

console.log(this.cache);

if (this.cache[num]) {
    return this.cache[num];
  }

if (num <= 1) {
    this.cache[num] = num;
    return num;
  } else {
    var sum = memoizedFibSum(num - 1) + memoizedFibSum(num - 2);
    this.cache[num] = sum;
    return sum;
  }
}

console.log(memoizedFibSum(0));
console.log(memoizedFibSum(1));
console.log(memoizedFibSum(3));
console.log(memoizedFibSum(10));
</script>

if (num <= 1) {
    this.cache[num] = num
    return num
  } else {
    const sum = memoizedFibSum(num - 1) + memoizedFibSum(num - 2)
    this.cache[num] = sum
    return sum
  }
}

console.log(memoizedFibSum(0))
console.log(memoizedFibSum(1))
console.log(memoizedFibSum(3))
console.log(memoizedFibSum(10))
</script></body>
</html>