SOURCE

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>
<ul>
      <li>A1</li>
      <li>A2</li>
</ul>
<ul>
   <li>B1</li>
   <li>B2</li>
</ul>
 
   <button id="shouBtn">显示</button>
    <button id="hideBtn">隐藏</button>
p {
  color: red;
}