js实现超简单的展开、折叠目录代码

<title>可折叠展开的简单目录</title>
<style>
div{
font-size:12px;
color:red;
background-color: #EAEAE8;
border: 1 solid #1892B5;
padding: 1
}
</style>
<div id="main1" style="color:blue" onclick="document.all.child1.style.display=(document.all.child1.style.display =='none')?'':'none'" > 
+ 主目录1</div> 
<div id="child1" style="display:none"> 
<a href="#">- 子目录1</a> <br> 
<a href="#">- 子目录2</a> <br> 
<a href="#">- 子目录3</a> <br> 
<a href="#">- 子目录4</a> 
</div> 
<div id="main2" style="color:blue" onclick="document.all.child2.style.display=(document.all.child2.style.display =='none')?'':'none'" > 
+ 主目录2 </div> 
<div id="child2" style="display:none"> 
<a href="#">- 子目录1</a> <br> 
<a href="#">- 子目录2</a> <br> 
<a href="#">- 子目录3</a> 
</div>