在线演示

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>属性操作-模拟短信发送内容保留</title>
<style>
#con {
width: 240px;
height: 200px;
background-color: #f1f1f1;
padding: 10px;
border: 1px solid #000;
overflow: hidden;
}
</style>
<script>
window.onload =function(){
var con = document.getElementById('con');
var txt = document.getElementById('txt');
var btn = document.getElementById('btn');
var oSpan = document.getElementById('oSpan');
btn.onclick = function(){
if(txt.value == ''){
alert('请输入点内容吧~');
}else{
con.innerHTML = con.innerHTML + oSpan.innerHTML + txt.value + '</br>';
txt.value = '';
}
}
}
</script>
</head>
<body>
<div id="con"></div>
<span id="oSpan">小明:</span>
<input type="text" id="txt">
<input type="button" value="提交" id="btn">
</body>
</html>