js设置随机切换背景图片

<script>

var imgs =["http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_2.jpg",
              "http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_default.png",
              "http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_3.jpg",
              "http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_1.jpg",
              "http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_4.jpg",
              "http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_5.jpg",
              "http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_6.jpg",
              "http://images.cnblogs.com/cnblogs_com/xiaobo-Linux/1112236/o_default-2.jpg",
              ];
var index=Math.round(Math.random()*7);
var img = imgs[index];

function showbg(){

document.body.style.backgroundImage="url("+img+")";

}
document.body.onload = function(){

showbg();
}

</script>