JavaScript的大数阶乘

一道算法题，以前51js上讨论过。思路就是自己实现乘法运算，如果用递归，如果求1000的阶乘就要出现脚本失控了

51JS上最为经典的方法：

   1: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

   2: <html xmlns="http://www.w3.org/1999/xhtml">

   3:  <head>

   4:   <title> new document </title>

   5:   <meta name="generator" content="editplus" />

   6:   <meta name="author" content="" />

   7:   <meta name="keywords" content="" />

   8:   <meta name="description" content="" />

   9:  </head>

10:

  11:  <body>

  12: <script type='text/javascript'>

  13: function factorial(n) {

  14:     var a = [1];

  15:     for (var i = 1;i<=n ;i++) {

  16:         for (var j = 0, c = 0;j<a.length || c != 0;j++ ) {

  17:             var m = (j < a.length) ? (i*a[j] + c) : c;

  18:             a[j] = m % 10;

  19:             c = (m - a[j]) / 10;

  20:         }

  21:     }

22:

  23:     return a.reverse().join("");

  24: }

25:

  26: var num = 1000;

27:

  28: alert(factorial(num));

  29: </script>

  30:  </body>

  31: </html>