01 jquery引入
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div id="app">小马哥</div>
<!--1.引包 -->
<script src="./jquery-3.5.1.js"></script>
<script>
var oDiv = document.getElementById('app');
console.log(oDiv);//<div id="app">小马哥</div>
//js对象转换jquery对象
console.log(jQuery(oDiv));
//$===jQuery
console.log($(oDiv));
console.log(jQuery);//jquery对象方法库
//jquery对象转换js对象
console.log(jQuery('#app')[0]);//<div id="app">小马哥</div>
console.log(jQuery('#app'))
</script>
</body>
</html>
