js获取html标签子节点内容及属性值

用原生javascript获取如下li标签中img的src属性值和span标签的date_url属性值

<script type="text/javascript">
var li=document.getElementById("li");
 
var src=li.firstChild.getAttribute("src");
alert(src);
 
var url=li.lastChild.getAttribute("date_url");
alert(url);
 
var name=li.lastChild.innerHTML;
alert(name);
</script>