​x
 
<!DOCTYPE html>
<html>
<head>
</head>
<body>
​
<h1>HTMLCollection item() 方法</h1>
​
<p>A P element.</p>
<p class="myclass">Another P element.</p>
<p class="myclass">A third P element.</p>
​
<p>单击按钮为 class="myclass" 的所有元素添加背景颜色：</p>
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<button onclick="myFunction()">设置颜色</button>
​
<script>
function myFunction() {
  var x, i;
  x = document.getElementsByClassName("myclass");
  for (i = 0; i < x.length; i++) {
  x.item(0).style.backgroundColor = "red";
  }
}
</script>
​
</body>
</html>
​