js遮罩层代码：
//显示div遮罩层
function showDivZhao(){
 if(!document.getElementById('divZhao')){
     var cEle = document.createElement("div");
     cEle.setAttribute("id","divZhao");
     cEle.setAttribute("style","background-color:black;z-index:1;position:absolute;left:0px;top:0px;width:100%;height:100%;opacity:0.4;filter:alpha(opacity=40);");
     document.body.appendChild(cEle);
 }
 else {
     document.getElementById('divZhao').style.display = "";
 }
}
//关闭div遮罩层
function closeDivZhao(){
 if(document.getElementById("divZhao")){
  document.getElementById("divZhao").style.display = "none";
 }
}
//窗口大小调整时
window.onresize = function () {
 if(document.getElementById("divZhao")){
     document.getElementById("divZhao").style.width = document.body.offsetWidth + "px";
     document.getElementById("divZhao").style.height = document.body.offsetHeight + "px";
 }
}