效果图：
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
<script src="js/jquery-3.3.1.js"></script>
</head>
<body>
<p><input type="checkbox" checked="checked" />多选框1</p>
<p><input type="checkbox" checked="checked"/>多选框2</p>
<p><input type="checkbox" checked="checked"/>多选框3</p>
<script>
$(function(){
$(":checkbox");
});
</script>
</body>
</html>