代码示例：

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
    </head>
    <body>
        <script>
            function jiecheng(a){
                var b =1
                for(;a>=1;a--){
                    b *=a
                }
                return b
            }
            var c = jiecheng(10)
            console.log(c)
            var d = jiecheng(12)
            document.write(d)
        </script>
    </body>
</html>

 

 代码示例：

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
    </head>
    <body>
        <script>
            function shulie(n){
                if(n===1 || n===2) return 1
                return shulie(n-1)+shulie(n-2)
            }
            var a=shulie(9)
            console.log(a)
        </script>
    </body>
</html>