Prototype - firstDescendant() 方法
此方法返回第一个子元素。这与 firstChild DOM 属性相反，后者将返回任何节点。
语法
element.firstDescendant();
返回值
它返回一个 HTML 元素。
示例
<html>
<head>
<title>Prototype examples</title>
<script type = "text/javascript" src = "/javascript/prototype.js"></script>
<script>
function showResult() {
desc = $('grandfather').firstDescendant();
alert("First Descendant is : " + desc.nodeName + ':' + desc.innerHTML );
child = $('grandfather').firstChild;
alert("First Child is : " + child.toString() );
}
</script>
</head>
<body>
<p>单击按钮查看结果。</p>
<div id = "grandfather">This is grand father
<div id = "father"> This is father.
<div id = "kid">This is kid</div>
</div>
</div>
<br />
<input type = "button" value = "showResult" onclick = "showResult();"/>
</body>
</html>
prototype_element_object.html
