<html><head><script type="text/javascript" src="/jquery/jquery.js"></script><script type="text/javascript">$(document).ready(function(){ $(".btn1").click(function(){ $("span").text($("p").width()); });});</script></head><body><p>本段落的宽度是 <span>unknown</span> px。</p><button class="btn1">获得宽度</button></body></html>