console 命令行工具 X clear

console

$("ul li:first-child").hide();
$("#showBtn").click(function(){
  $("ul li:first-child").show();
  });
$("#hideBtn").click(function(){
  $("ul li:first-child").hide();
  });

<h1>heading</h1>
<p>paragraph</p>
<p>paragraph 2</p>
<ul>
  <li>A1</li>
  <li>A2</li>
  </ul>
<ul>
  <li>B1</li>
  <li>B2</li>
  </ul>
<button id="showBtn">显示</button>
<button id="hideBtn">隐藏</button>

p{
  color:orange;
}