js用定时器几句话实现双色球开奖效果

<!DOCTYPE html>
<html lang="zh">
	<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></title>
		<style type="text/css">
			* {
				margin: 0;
				padding: 0;
			}

			button {
				width: 80px;
				height: 30px;
				margin: 40px;
			}

			div>span {
				display: inline-block;
				width: 60px;
				height: 60px;
				background-color: red;
				font-size: 28px;
				line-height: 60px;
				text-align: center;
				color: #fff;
				border-radius: 50%;
				margin: 6px;
			}
		</style>
		<script type="text/javascript">
			window.onload = function() {
				var btnS = document.getElementsByTagName('button');
				var ballS = document.getElementsByTagName('span');
				var timer = null;

				btnS[0].onclick = function() {
					btnS[0].disabled = true;
					btnS[1].disabled = false;
					timer = setInterval(sj, 40);
				}

				btnS[1].onclick = function() {
					console.log(idx);
					if(idx >=6){
						idx=0;
						btnS[0].disabled = false;
						btnS[1].disabled = true;
						clearInterval(timer);
						return 0;
					}
					setTimeout(function() {
						idx++;
					}, 1000);
					
				}
				var idx = 0;

				function sj() {
					for (var i = idx; i < 7; i++) {
						a = Math.floor(Math.random() * 100);
						ballS[i].innerText = a;
					}

				}

			}
		</script>
	</head>
	<body>
		<button type="button">开始</button>
		<button type="button">停止</button>
		<div>
			<span></span>
			<span></span>
			<span></span>
			<span></span>
			<span></span>
			<span></span>
			<span></span>
		</div>
	</body>
</html>