index.html

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>666</title>
		<style type="text/css">
			.div1{
				width: 500px;
				height: 300px;
				overflow-y: scroll;
				margin: auto;
				border: 1px solid red;
			}
			.div2{
				width: 200px;
				height: 50px;
				border: 1px solid red;
			}
			
			
		</style>
	</head>
	<body>
		
		<div class="div1">
			666
		</div>
		
		<button type="button" id="btn">添加</button>
		
		<script type="text/javascript">
			var div1 = document.querySelector('.div1');
			var btn = document.querySelector('#btn');
			btn.addEventListener('click',function(){
				console.log('66')
				var k = div1.innerHTML;
				div1.innerHTML = k+"<br/>66";
	
				div1.scrollTop = div1.scrollHeight;
				
			})
		</script>
	</body>
</html>