比如说：
btn.onclick =function (){}这个就不行
btn.onmouseover =function (){}这个就可以运行
反正换成其他事件都可以，就是onclick用不了，也没报错
似乎没啥问题 。我点击生效了
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<button id="btn">888</button>
</body>
<script>
let btn = document.getElementById("btn");
btn.onclick = function () {
alert("99")
}
</script>
</html>
onclick事件可以生效啊，你这样写吧
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
div{
/* margin-top: 3px; */
/* margin-bottom: 3px; */
height: 100px;
width:100px;
border-radius: 10px;
background-color: green;
/* line-height:center; */
position: absolute;
display: block;
}
</style>
<script type="text/javascript">
var count=0;
function move(){
alert("你好");
}
</script>
</head>
<body>
<button id="btn" onclick="move()">点我弹框</button><br>
</body>
</html>
记得把<button>的标签加个type=button试试，即<button type='button'>，或许能好
```