var lis=document.getElementsByTagName("li");
    function Change(obj){
        for(var i=1;i<lis.length;i++){
            if(lis[i].onmouseover==null && lis[i].onmouseout==null){
              lis[i]=this;
              lis[i]. onmouseover=function(){this.style.background='#FAFAFA'};
              lis[i].onmouseout=function(){this.style.background=''};
              getFirstChild(lis[i]).style.visibility="hidden";
            }  
            if(lis[i].id == obj.id){  
              obj.style.background='blue';
              obj.onmouseover="";
              obj.onmouseout=""; 
              getFirstChild(obj).style.visibility="visible";
            }else{  
              lis[i].style.background='';
            }  
          }
    }
//获取指定节点的第一个子节点    
function getFirstChild(obj) {
    var result = obj.firstChild; 
    while (!result.tagName) { 
    result = result.nextSibling; 
    } 
    return result; 
} 

        <div id="play_list">
          <div class="divScroll">
            <ul style="list-style:none">
                <li class="pl-title">播放列表：</li>
                <?php for($i=0;$i<30;$i++){ ?>
                <li id="pl-<?php echo $i ?>" onmouseover="this.style.background='#FAFAFA';" onmouseout="this.style.background='';" onclick="Change(this);">
                <img class="pl-img" src="../images/music.gif" />
                <a href="#">Katy Perry - The One That Got Away</a>
                </li>
                <?php } ?>
            </ul>
          </div>
        </div>