下拉菜单的实现，附图说明
下拉1与下拉2的点击独立，展开菜单后自动调整页面长度，含三角形方向变化
经常在网页上看到这种效果，不知道怎么实现，
本人绝对菜鸟，求指教
[解决办法]
- HTML code
<!DOCTYPE HTML><html> <head> <meta charset="gb2312" /> <title></title> <style> * { margin:0; padding:0; font-size:14px; } ul { list-style:none; } .arr { display:inline-block; position:absolute; left:40px; top:9px; width:0; height:0; overflow:hidden; border:5px dashed transparent; } .arr-t { border-top:5px solid #000; _border-width:4px; } .arr-b { top:4px; border-bottom:5px solid #000; } .bar { margin:100px; } .bar li { position:relative; margin-top:4px; padding:4px 6px; width:80px; border:1px solid #999; cursor:pointer; } .bar li div { padding-left:10px; } </style> </head> <body> <ul class="bar" id="bar"> <li> 菜单<span class="arr arr-t"></span> <div style="display:none;"> 1-1<br /> 1-1<br /> 1-1<br /> </div> </li> <li> 菜单<span class="arr arr-t"></span> <div style="display:none;"> 1-1<br /> 1-1<br /> 1-1<br /> </div> </li> </ul> <script> var $ = function(id){ return document.getElementById(id); }; var $t = function(tag, cot){ cot = cot || document; return cot.getElementsByTagName(tag); }; var objs = $t('li', $('obj')); for(var i = 0, len = objs.length; i < len; i++){ objs[i].onclick = function(){ var d = $t('div', this)[0]; var s = $t('span', this)[0]; if( d.style.display == 'none' ){ d.style.display = 'block'; s.className = s.className.replace('arr-t', 'arr-b'); }else{ d.style.display = 'none'; s.className = s.className.replace('arr-b', 'arr-t'); } } } </script> </body></html>