代码示例:(标识:eg_js_dom_getelementsbyclassname)
<!DOCTYPE html>
<html>
<body>

<h1>通过类名查找 HTML 元素</h1>

<p>Hello World!</p>

<p class="intro">DOM 很有用。</p>

<p class="intro">本例演示 <b>getElementsByClassName</b> 方法。</p>

<p id="demo"></p>

<script>
var x = document.getElementsByClassName("intro");
document.getElementById("demo").innerHTML = 
'class ="intro" 的第一段(索引 0):' + x[0].innerHTML;
</script>

</body>
</html>
运行结果: