定时出现和消失的层

 <script type="text/javascript">
<!--
        /*
        message:要显示的消息
        x,y:显示消息框的坐标,默认为左上角
        delay:延迟多长时间消失，-1为永不消失，单位为毫秒
        */
        function feedBackMessage(message, x, y, delay) {
            if (!message) return;
            //只允许百分数或数值参数
            x = /\d{1,2}%|100%|left|right/.test(x) ? x : (parseInt(x) || 0) + "px";
            y = /\d{1,2}%|100%|top|bottom/.test(y) ? y : (parseInt(y) || 0) + "px";
            delay = parseInt(delay) || -1;
            var fdDiv = document.getElementById('show_feedBack_message');
            if (!fdDiv) {
                var showMessage = document.createElement("<div id='show_feedBack_message' style='z-index:10000;filter:alpha(opacity=100);position:absolute;white-space:nowrap'><img src='/images/loading22.gif'/></div>");
                document.body.appendChild(showMessage);
                fdDiv = document.getElementById('show_feedBack_message');
            }

            if (feedBackMessage.timer) { clearInterval(feedBackMessage.timer) }
            fdDiv.innerText = message;
            fdDiv.style.display = "";
            var docWidth = document.documentElement.scrollWidth > document.documentElement.clientWidth ? document.documentElement.scrollWidth : document.documentElement.clientWidth;
            var docHeight = document.documentElement.scrollHeight > document.documentElement.clientHeight ? document.documentElement.scrollHeight : document.documentElement.clientHeight;
            if (/left|right/.test(x)) {
                x = (x == "left") ? "0px" : (docWidth - fdDiv.offsetWidth) + "px";
            }
            if (/top|bottom/.test(y)) {
                y = (y == "top") ? "0px" : (docHeight - fdDiv.offsetHeight) + "px";
            }
            fdDiv.style.left = x;
            fdDiv.style.top = y;
            fdDiv.filters.Alpha.Opacity = 100;

            //渐隐效果
            var step = parseInt(delay / 100);
            var alpha = fdDiv.filters.Alpha.Opacity;
            if (delay != -1) {
                feedBackMessage.timer = setInterval(function() {
                    if (fdDiv.filters.Alpha.Opacity > 0) {
                        fdDiv.filters.Alpha.Opacity--
                    } else {
                        clearInterval(feedBackMessage.timer);
                        fdDiv.style.display = "none"
                    }
                }, step);
            }
        }
//-->
</script>