递归函数

 1 window.onload = function() {
 2     var a = factorial;
 3     factorial = null;
 4     alert(a(4));
 5 };
 6 
 7 /**
 8  * 叠乘
 9  * @param  {叠乘的基数} num   n
10  * @return {叠乘结果}         n*(n-1)*(n-2)*...*1
11  */
12 var factorial = (function f(num){
13     if (num <= 1) {
14         return 1;
15     }else{
16         return num * f(num - 1);
17     }
18 });