上传或下载等待时动态添加提示“正在加载图片”

[javascript]代码库

 function showImg() {
      
            var newMask = document.createElement("div"); //加载一个蒙层，防止点击
            newMask.style.position = "absolute";
            newMask.style.zIndex = "1";
            newMask.style.width = document.body.scrollWidth + "px"; //适应文档宽度
            newMask.style.height = document.body.clientHeight+"px";//适应文档高度
            newMask.style.top = "0px";
            newMask.style.left = "0px";
            newMask.style.backgroundColor = "#fff";//背景色
            newMask.style.filter = "alpha(opacity=40)";
            newMask.style.opacity = "0.40";//透明度
            newMask.style.display = "block";
            newMask.style.textAlign = "center";
            newMask.style.paddingTop = document.body.clientHeight / 2 + "px";
            document .append(newMask);
            $("body").append("<img  src='../images/jiazai2.gif'/>");
            var imgd = document.getElementsByTagName("img")[0];
            imgd.style.position = "absolute";//图片定位
            imgd.style.zIndex = "9999";
            imgd.style.top = document.body.clientHeight / 2+ "px";
            imgd.style.left = document.body.scrollWidth/2-50 + "px";
        }