换背景——点击按钮定时更换背景图片,点击按钮停止

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>

<body>

<input type="button" value="换背景吧" />
<input type="button" value="停" />

<script>
var aBtn = document.getElementsByTagName('input');
var arrUrl = [ 'img/1.jpg', 'img/2.jpg', 'img/3.jpg', 'img/4.jpg' ];
var num = 0;
var timer = null;

var oBody = document.body;

aBtn[0].onclick = function (){
    
    clearInterval( timer );            // null、未定义
    
    timer = setInterval(function(){
        oBody.style.background  = 'url('+ arrUrl[num] +')';
        num++;
        num%=arrUrl.length;
    }, 1000);
};
aBtn[1].onclick = function (){
    clearInterval( timer );
};


</script>

</body>
</html>

 

posted @ 2017-03-21 17:17  念念念不忘  阅读(344)  评论(0)    收藏  举报