<script language="javascript" type="text/javascript">

    
    
 var docEle = function() 
    {
        return document.getElementById(arguments[0]) || false;
    }
    
 function openNewDiv(_id) {
  var m = "mask";
  if (docEle(_id)) document.removeChild(docEle(_id));
  if (docEle(m)) document.removeChild(docEle(m));
  // 新激活图层
  var newDiv = document.createElement("div");
  newDiv.id = _id;
  newDiv.style.position = "absolute";
  newDiv.style.zIndex = "9999";
  newDiv.style.width = "500px";
  newDiv.style.height = "300px";
  newDiv.style.top = "50px";
  newDiv.style.left = (parseInt(document.body.scrollWidth) - 300) / 2 + "px"; // 屏幕居中
  newDiv.style.background = "#EFEFEF";
  newDiv.style.border = "1px solid #860001";
  newDiv.style.padding = "5px";
  newDiv.innerHTML = "新激活图层内容&nbsp;&nbsp;&nbsp;&nbsp;";
  document.body.appendChild(newDiv);
  // mask图层
  var newMask = document.createElement("div");
  newMask.id = m;
  newMask.style.position = "absolute";
  newMask.style.zIndex = "1";
  newMask.style.width = document.body.scrollWidth + "px";
  newMask.style.height = document.body.scrollHeight + "px";
  newMask.style.top = "0px";
  newMask.style.left = "0px";
  //newMask.style.background = "#000";
  newMask.style.filter = "alpha(opacity=40)";
  newMask.style.opacity = "0.40";
  document.body.appendChild(newMask);

  // 关闭mask和新图层
  var newA = document.createElement("a");
  newA.href = "#";
  newA.innerHTML = "关闭";
  newA.onclick = function() {
   document.body.removeChild(docEle(_id));
   document.body.removeChild(docEle(m));
   return false;
  }
  newDiv.appendChild(newA);
 }
 
        </script>
            

 <a href="#" onclick="openNewDiv('newDiv');return false;">激活新层</a>