function getTotal(n){
  let s = 1,total;
  while(s<=n){
    total = 1*s;
    s++;
  }
  return total
}

const stepNum = (num) => (num === 1 ? num : num * stepNum(num - 1));

console.log(stepNum(3))
console.log(stepNum(4))
console.log(stepNum(5))
console.log(stepNum(6))

const getFactorial = n => {
	return new Array(n-1).join(',').split(',').reduce( total => { --n;  return total*n}, n)
}

function getN(num) {
  return Array.from(new Array(num)).reduce((cacheNum, it, index) => {
    return cacheNum * (index + 1);
  }, 1);
}
console.log(getN(6));

const factorial = num => {
  if (num > 1) 
    return num * factorial(num - 1)
  return 1
}

console.log(factorial(5))

    function factorial(num) {
        let data = num;
        if (num < 0) return -1;
        if (num === 0 || num === 1) return 1;
        while (num > 1) {
            num--;
            data *= num;
        }
        return data;
    }

    console.log(factorial(5));  // 120

function tailDiGui(n, r) {
    if (n === 1) {
        return r;
    } else {
        return tailDiGui(n - 1, r * n)
    }
}

function jieCheng(n) {
    return tailDiGui(n, 1)
}
console.log(jieCheng(100));

function factorial(n) {
    if (isFinite(n) && n > 0 && Math.round(n)) {
        if (!(n in factorial)) {
            factorial[n] = n * factorial(n - 1)
        }

        return factorial[n]
    } else {
        return NaN;
    }
}

factorial[1] = 1;

console.log(factorial(1000));

function factorial (n) {
  if (n >  1) {
    return n * factorial(n - 1)
  }
  return 1
}

factorial(0) // 1
factorial(5) // 120