<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<input type="text" id="number" placeholder="请输入数字"><br>
<button id="btn">=</button><br>
<input type="text" id="result" placeholder="它的阶乘是">
<script>
//1.获取元素值
btn.onclick=function(){
var n=number.value-0;
sum=1
//计算数字阶乘
for(var i=n;i>=1;i--){
sum*=i;
}
result.value=sum;
}
</script>
</body>
</html>