javaScritp递归求n的阶乘

<script type="text/javascript">
	function factorial(n){
		if(typeof(n)=="number"){
			if(n==1){
				return 1;
			}
			else{
				return n*factorial(n-1);
			}
		}else{
			alert("你输入的参数类型不正确！");
		}
	}
	alert(factorial(4));
</script>