用递归实现一个阶乘算法5! = 5 * 4 * 3 * 2 * 1 = 120用递归function factorial(n) {    if (n === 0) {        return 1;    } else {        return n * factorial(n - 1);    }} 用栈操作function fact(n) {    var s = new Stack();    while (n > 1) {        //[5,4,3,2]        s.push(n--);    }    var product = 1;    while (s.length() > 0) {        product *= s.pop();    }    return product;}fact(5) //120