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

<h1>JavaScript HTML DOM</h1>

<p>Hello World!</p>

<p>Hello China!</p>

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

<script>
var myCollection = document.getElementsByTagName("p");
document.getElementById("demo").innerHTML = 
"此文档包含 " + myCollection.length + " 段文字。";
</script>

</body>
</html>
运行结果: