<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style type="text/css">
#btn1:hover,#btn2:hover {
background: red;
}
</style>
</head>
<body>
<input type="button" value="开启" />
<input type="button" value="关闭" />
<script>
var obtn1=document.getElementById('btn1');
var obtn2=document.getElementById('btn2');
var timer=null;
obtn1.onclick=function()
{
timer=setInterval(function() //开启循环：每秒出现一次提示框
{
alert('a');
},1000);
}
obtn2.onclick=function()
{
clearInterval(timer); //关闭循环
}
</script>
</body>
</html>