Result Size: 625 x 534
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<!DOCTYPE html>
<html>
<body>
<h2>按类名查找 HTML 元素</h2>
<p>Hello World!</p>
<p class="intro">DOM 非常有用。</p>
<p class="intro">此示例演示了 <b>getElementsByClassName</b> 方法。</p>
<p id="demo"></p>
<script>
var x = document.getElementsByClassName("intro");
document.getElementById("demo").innerHTML = 
'第一段(索引为 0)带有 class="intro":' + x[0].innerHTML;
</script>
</body>
</html>