jqurey定位 id

//---$("")直接写单词是这类标签的事件，#加某ID指某特定控件

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>window-ready</title>
<script type="text/javascript" src='JAVASCRIPT/jquery-3.2.1.min.js'></script>
<script>
$(document).ready(function (){
$("#btn").click(function (){
alert('luhan');
});
});

</script>

</head>
<body>
<hr style='border:5px dotted GREEN'>

<button id='btn' name='btn' value='hongyan'>hongyan</button>