$( "<p></p>“)和”<p></p>“之间的差异

Question

我在学习示例中使用了var foo和var $foo，但无法区分它们：

<p id="css">CSS (Cascading Style Sheets) is a representation style sheet language.</p>

<script src="https://cdn.jsdelivr.net/npm/jquery@3.2.1/dist/jquery.min.js"></script>
<script>

$(document).ready(function(){
    var js = "<p id='js'>JavaScript often abbreviated as JS, is a high-level, interpreted programming language.</p>";
    var $jquery = $("<p id='jquery'>jQuery is a cross-platform JavaScript library designed to simplify the client-side scripting of HTML.</p>");
    $("#css").after(js);
    $("#css").after($jquery);
})
</script>

在上面的最小代码中，当执行像$().html, $().before()这样的插入操作时，它们的功能是相同的。