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:red;}