<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
#box{width:300px;height:400px;margin: 20px auto;border: solid 1px black}
#box #box1{height: 300px;border-bottom: solid 1px black;overflow: auto;}
#box1 div{max-width:220px;margin: 4px;padding: 4px;border-radius: 6px;clear: both;}
#box1 div:nth-child(2n){background: cornflowerblue;float: left;}
#box1 div:nth-child(2n-1){background: darkcyan;float: right}
#box #btns{height: 99px}
#btns *{height: 99px;border: none;padding: 0;margin: 0;background: none;float: left;}
#txt{width: 260px;padding: 20px;box-sizing: border-box}
#btn{width: 40px;border-left: solid 1px black;}
</style>
</head>
<body>
<div id="box">
<div id="box1"></div>
<div id="btns">
<textarea id="txt"></textarea>
<input type="button" value="发送" id="btn">
</div>
</div>
<script>
var btnObj = document.getElementById("btn");
var box1Obj = document.getElementById("box1");
var txtObj = document.getElementById("txt");
btnObj.onclick = ()=>{
if(txtObj.value == ""){
alert("输入错误");
}else{
var div = document.createElement("div");
div.innerHTML = txtObj.value;
box1Obj.appendChild(div);
box1Obj.scrollTop = box1Obj.scrollHeight;
txtObj.value = "";
}
}
</script>
</body>
</html>