<script>
function getSum(x) {
if(x == 1){
return 1;
}else{
return x*getSum(x-1);
}
}
var i;
i = prompt("请输入一个求阶乘的数：")
while(i == '' || isNaN(i) || i == " "){
alert("输入错误，请重新输入！");
i = prompt("请输入一个求阶乘的数：")
}
if(i == 0){
alert("0的阶乘是：0")
}
getSum(i);
alert(i+"的阶乘是："+getSum(i));
</script>
