孤独的对话

效果：

思路：

不想分析了，能用就行

<!DOCTYPE html>
<html lang="en">
<head>
  <link rel="shortcut icon" href="#" />
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
    }
    .container {
      padding-top: 15px;
      margin: 30px;
      width: 300px;
      height: 350px;
      background-color:burlywood;
      overflow-y: scroll;
      scrollbar-width: none; /* firefox */
      -ms-overflow-style: none; /* IE 10+ */
    }
    .container::-webkit-scrollbar {
      display: none; /* Chrome Safari */
    }
    .leftbox {
      width: 180px;
      height: 30px;
      padding-left: 8px;
      line-height: 30px;
      background-color: bisque;
      border-radius: 22px;
      list-style-type: none;
      margin-bottom: 15px;
    }
  </style>
</head>
<body>
  <ul class="container">
    <li class="leftbox">我是一个小小鸟~~~</li>
  </ul>
  <script>
    let container = document.getElementsByClassName("container")[0];
    let boxarr = []
    for( let i = 0 ;i < 12; i++ ) {
      let box = document.createElement("li");
      box.innerHTML  = i+1+".我是一个小小鸟~~~";
      box.classList.add("leftbox");
      boxarr.push(box);
    }
    let step = 0
    let a = setInterval( ()=> {
      container.appendChild(boxarr[step]);
      step++;
      let { scrollHeight,offsetHeight } = container;
      console.log("scrollHeight："+scrollHeight);
      console.log("offetHeight"+ offsetHeight);
      
      if ( scrollHeight > offsetHeight ) {
        container.scrollTop = scrollHeight-offsetHeight;
        console.log("scrollTop:"+ container.scrollTop);
      } 
      if ( step > 11) clearInterval(a);
      
    },1000)
  </script>
</body>
</html>