javascript如何获得span的id呢

如何获得span的id呢。
比如说<li><span class="folder" id="1">Folder 2</span>
<ul>
<li><span class="folder" id="2">Subfolder 2.1</span>
<ul id="folder21">
<li><span class="file" id="3">File 2.1.1</span></li>
<li><span class="file" id="4">File 2.1.2</span></li>
</ul>
</li>
<li><span class="file" id="5">File 2.2</span></li>
</ul>
</li>
如何获得呢？谢谢了

解决方案 »

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var spans = document.getElementsByName("span");
for(var i=0;i<spans.length;i++){
   alert(spans[i].id);
}
不好意思写错了
应该是
var spans = document.getElementsByTagName("SPAN");
for(var i=0;i<spans.length;i++){
    alert(spans[i].id);
}
说错了。如何在鼠标点这个span的时候，就获得这个span的id呢。比如点li><span class="file" id="3">File 2.1.1</span></li>
获得id=3,弹出警告说是id=3我打算用来做tree的。谢谢了
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<script type="text/javascript">
function clicks(el){
alert(el.id);
}
</script>
</HEAD><BODY>
<li><span class="folder" id="1" onclick="clicks(this)">Folder 2</span>
<ul>
<li><span class="folder" id="2" onclick="clicks(this)">Subfolder 2.1</span>
<ul id="folder21">
<li><span class="file" id="3" onclick="clicks(this)">File 2.1.1</span></li>
<li><span class="file" id="4" onclick="clicks(this)">File 2.1.2</span></li>
</ul>
</li>
<li><span class="file" id="5" onclick="clicks(this)">File 2.2</span></li>
</ul>
</li>
</BODY>
</HTML>
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebForm._Default" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<meta http-equiv="content-type" content="text/html; charset=UTF-8" />
  <title>test</title>
  <script type="text/javascript">
      function clickEvent(control)
      {
        alert(control.id);
      }
  </script>
</head>
<body>
  <form id="form1" runat="server">
    <span id="span1" onclick="clickEvent(this);">File 11</span>
  </form>

</body>
</html>
楼上的可以jquery不是更好吗<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>5_14</title>
<script src="jquery-1.3.2.js"></script>
<script language="javascript" type="text/javascript">
$(document).ready(function(){
$(".file").click(function(){
alert($(this).attr("id"))
});
$(".folder").click(function(){
alert($(this).attr("id"))
});
});
</script>
</head><body>
<li><span class="folder" id="1">Folder 2</span>
    <ul>
        <li><span class="folder" id="2">Subfolder 2.1</span>
            <ul id="folder21">
                <li><span class="file" id="3">File 2.1.1</span></li>
                <li><span class="file" id="4">File 2.1.2</span></li>
            </ul>
        </li>
        <li><span class="file" id="5">File 2.2</span></li>
    </ul>
</li>
</body>
</html>
<li><span class="folder" id="1">Folder 2</span>
<ul>
<li><span class="folder" id="2">Subfolder 2.1</span>
<ul id="folder21">
<li><span class="file" id="3">File 2.1.1</span></li>
<li><span class="file" id="4">File 2.1.2</span></li>
</ul>
</li>
<li><span class="file" id="5">File 2.2</span></li>
</ul>
</li>
<script>
    window.onload=function (){
        var obj=document.getElementsByTagName("span");
        for(var i=0;i<obj.length;i++)
            obj[i].onclick=function(){alert(this.id);};
    }
</script>