js等待效果

function showloading(){
	var loaddiv;
	if(loaddiv=document.getElementById("loaddiv")){
		loaddiv.style.display = "block";
	}else{
	    loaddiv = document.createElement("DIV");
	    loaddiv.id="loaddiv";
	    loaddiv.style.position = "absolute";
	    loaddiv.style.zIndex = 1000;
	    loaddiv.style.display="";
	    loaddiv.style.left = 0;
	    loaddiv.style.top  = 0;
	    loaddiv.style.border = "1px solid gray"
	    loaddiv.style.background = "#ffffff"
	    loaddiv.style.padding = "5";
	}
	
	var scrollTop=0;
    if(top.document.documentElement && top.document.documentElement.scrollTop){
        scrollTop = top.document.documentElement.scrollTop;
    }else if(document.body){
        scrollTop = top.document.body.scrollTop;
    }
    
    var scrollWid = document.body.scrollWidth/2-50;
    
    loaddiv.style.left = scrollWid+"px";
    loaddiv.style.top  = (scrollTop + 5)+"px" ;
    
    loaddiv.innerHTML = "<img src='/images/loading.gif'><h>数据正在获取，请稍等。。。</h>";
    document.body.style.cursor="wait";  
    
    
  var sWidth,sHeight;
  sWidth=document.body.scrollWidth;//浏览器工作区域内页面宽度 或使用 screen.width//屏幕的宽度
  sHeight=document.body.scrollHeight;//屏幕高度（垂直分辨率）


  //背景层（大小与窗口有效区域相同，即当弹出对话框时，背景显示为放射状透明灰色）
  var bgObj=document.createElement("div");//创建一个div对象（背景层） //动态创建元素，这里创建的是 div
  //定义div属性，即相当于(相当于，但确不是，必须对对象属性进行定义
  //<div id="bgDiv" style="position:absolute; top:0; background-color:#777; filter:progid:DXImagesTransform.Microsoft.Alpha(style=3,opacity=25,finishOpacity=75); opacity:0.6; left:0; width:918px; height:768px; z-index:10000;"></div>
  bgObj.setAttribute('id','bgDiv');
  bgObj.style.position="absolute";
  bgObj.style.top="0";
  bgObj.style.background="#ffffff";
  bgObj.style.filter="progid:DXImageTransform.Microsoft.Alpha(style=3,opacity=25,finishOpacity=75";
  bgObj.style.opacity="0.6";
  bgObj.style.left="0";
  bgObj.style.width=sWidth + "px";
  bgObj.style.height=sHeight + "px";
  bgObj.style.zIndex = "10000";
  document.body.appendChild(bgObj);//在body内添加该div对象
    
  document.body.appendChild(loaddiv);
}