<html>
<head>
<script type="text/javascript" src="/jquery/jquery.js"></script>
<script type="text/javascript">
$(document).ready(function(){
$("button").click(function(){
$(".122").prepend("<b>Hello world!</b> ");
});
});
</script>
</head>
<body>
<div class="122"
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
</div>
<button>在每个 p 元素的开头插入内容</button>
</body>
</html>