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

<h1>Finding HTML Elements by Class Name</h1>

<p class="intro">Hello World!</p>
<p class="intro">Hello China!</p>
<p class="intro">Hello Shanghai!</p>

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

<script>
var myElements = document.getElementsByClassName("intro");
document.getElementById("demo").innerHTML = "类名为 intro 的第三段文本是:" + myElements[2].innerHTML;
</script>

</body>
</html>
运行结果: