HTML代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>练习</title>
<script src="jquery-3.3.1.js"></script>
<script src="text3.js"></script>
<!--库的引用必须要先于自己的-->
</head>
<body>
<button>老哥，点我</button>
</body>
</html><!DOCTYPE html>
<html lang="en
