Wrote a super simple code
<html>
<head>
<script src="jquery-3.3.1.min.js"></script>
<script type="text/javascript">
$("#btn").click(function(){
alert("eeeeee");
});
</script>
</head>
<body>
<input type="button" id="btn" value="点我">
</body>
</html>
As a result, the click did not respond, and there was nothing wrong. There was no response. I wondered for a long time. It turned out that the js was placed in $("document").ready(function() {});
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script src="jquery-3.3.1.min.js"></script>
<script type="text/javascript">
$("document").ready(function() {
$("#btn").click(function(){
alert("eeeeee");
});
});
</script>
</head>
<body>
<input type="button" id="btn" value="点我">
</body>
</html>