自动切换背景图片

<script type="text/javascript">
    var img = Math.round(Math.random() * 10);
    var Img = new Array();
    //需要加载的背景图片
    Img[0] = "https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=3735316392,212988712&fm=200&gp=0.jpg"
    Img[1] = "https://ss1.bdstatic.com/70cFuXSh_Q1YnxGkpoWK1HF6hhy/it/u=4165415060,2023874983&fm=26&gp=0.jpg"
    Img[2] = "https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=3706677817,1678627265&fm=26&gp=0.jpg"
    Img[3] = "https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=518541639,428272303&fm=26&gp=0.jpg"
    Img[4] = "https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=1482498295,222129637&fm=26&gp=0.jpg"
    Img[5] = "https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=357843698,3560590396&fm=26&gp=0.jpg"
    Img[6] = "https://ss1.bdstatic.com/70cFvXSh_Q1YnxGkpoWK1HF6hhy/it/u=1377601590,3543048053&fm=200&gp=0.jpg"
    Img[7] = "https://ss3.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=4189220961,2869949368&fm=26&gp=0.jpg"
    Img[8] = "https://ss1.bdstatic.com/70cFuXSh_Q1YnxGkpoWK1HF6hhy/it/u=3004924597,1854631352&fm=26&gp=0.jpg"
    Img[9] = "https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=299724880,3285215622&fm=26&gp=0.jpg"
    Img[10] = "https://ss1.bdstatic.com/70cFuXSh_Q1YnxGkpoWK1HF6hhy/it/u=2326892196,580815977&fm=26&gp=0.jpg"
    if(document.readyState === "loading" ||document.readyState === "interactive" ||document.readyState === "complete")
    {
        document.body.style.backgroundRepeat = "no-repeat";
        document.body.style.position = "center center" ;
        document.body.style.backgroundAttachment = "fixed";
        document.body.style.backgroundSize = "cover";
        document.body.style.backgroundImage = "URL("+Img[img]+")";
    }
</script>