JavaScript实现网页留言板功能

<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>留言发布</title>
  <style>
    body {
      margin: 200px;
    }
    *{
      margin: 0px;
      padding: 0px;
    }
    li {
      list-style: none;
      width: 500px;
      height: 30px;
      margin-top: 5px;
      border: 1px solid black;
      background-color: pink;
    }
    textarea{
      width: 200px;
      height: 80px;
    } 
  </style>
</head>
<body>
  <textarea name="" id=""></textarea>
  <button>发布</button>
  <ul>
    
  </ul>
  <script>
    //获取元素
    var btn = document.querySelector('button');
    var text = document.querySelector('textarea');
    var ul = document.querySelector('ul');
    //注册时间
    btn.onclick = function(){
      if(text.value == ''){
        alert("您没有输入内容。")
        return false;
      }else{
        var li = document.createElement('li');
        li.innerHTML = text.value;
        //ul.appendChild(li);
        ul.insertBefore(li,ul.children[0])
      }
      text.value='';
      
    }
  </script>
</body>
</html>