Div 弹出屏幕居中

JS控制id 为"divv"的层在屏幕中间

function show(){

　　var width=document.getElementById("divv").style.width;

　　var height=document.getElementById("divv").style.height;

　　with(document.getElementById("divl").style){  
          left = (window.screen.width-width)/2+document.documentElement.scrollLeft;
          top  = (window.screen.height-height)/2+document.documentElement.scrollTop;
          position='absolute'
          zIndex = 1001
      }  

　　document.getElementById("divv").style.display = "block";

}