​x
 
<!DOCTYPE html>
<html>
<style>
.myStyle {
  background-color: coral;
  padding: 16px;
}
</style>
​
<body>
<h1>Element 对象</h1>
​
<h2>className 属性</h2>
​
<button onclick="myFunction()">更改</button>
<p>如果 "myDIV" 有 "myStyle" 类，那么点击“更改”可修改其字体大小。</p>
​
<div id="myDIV" class="myStyle">
<p>我是 myDIV。</p>
</div>
​
<script>
function myFunction() {
  const element = document.getElementById("myDIV");
  if (element.className == "myStyle") { 
    element.style.fontSize = "30px";
  }
}
</script>
​
</body>
</html>
​