js飘窗

广告页上总会出现飘窗效果：

adver_pos_id = getOtherParameter("id");

adver_Sid = getOtherParameter("Sid");

document.write("<div id='fudong01' style='position:absolute;z-index:50000;'><a onClick='setNone(fudong01)' style='position:absolute;right:0px;top:-18px;cursor:pointer;display:block;48px;height:16px;font-size: 12px;color:#fff;text-align:center;background:#333;border:1px solid #999;overflow:hidden;font-family:宋体;'>×关闭</a><img src='images/pf.png' border='0' /></div>");

function setNone(str_fd) {
    str_fd.style.display = "none";
}

var x = 0,
y = 0

var xin = true,
yin = true

var step = 3

var delay = 100; //设置滚动时间 
var obj = document.getElementById("fudong01")

function floatAD() {

    var L = 0;

    var T = 0;

    var cw = document.documentElement.clientWidth || document.body.clientWidth;

    var ch = document.documentElement.clientHeight || document.body.clientHeight; //处理浏览器对document.body的兼容问题
    var R = (cw - obj.offsetWidth) / 2

    var B = ch - obj.offsetHeight;

    y++;

    var atop = 0;

    obj.style.left = x + document.body.scrollLeft + "px";

    if (document.documentElement.scrollTop == 0) {

        atop = document.body.scrollTop;

    } else {

        atop = document.documentElement.scrollTop

    }

    obj.style.top = y + atop + "px"

    x = x + step * (xin ? 1 : -1)

    if (x < L) {
        xin = true;
        x = L
    }

    if (x > R) {
        xin = false;
        x = R
    }

    y = y + step * (yin ? 1 : -1)

    if (y < T) {
        yin = true;
        y = T
    }

    if (y > B) {
        yin = false;
        y = B
    }

}

var itl = setInterval("floatAD()", delay)

obj.onmouseover = function() {
    clearInterval(itl)
}

obj.onmouseout = function() {
    itl = setInterval("floatAD()", delay)
}