JS弹出遮罩层

// create div
var mask=document.createElement("div");
mask.id="mask";
mask.style.position="absolute";
mask.style.filter="progid:DXImageTransform.Microsoft.Alpha(style=4,opacity=25)";//IE的不透明设置
mask.style.opacity=0.4;//Mozilla的不透明设置
mask.style.background="black";
mask.style.top="0px";
mask.style.left="0px";
mask.style.width="10000px";
mask.style.height="888px";
mask.style.zIndex=1000;
document.body.appendChild(mask);

//delete div
var mask=document.getElementById("mask");
if(null==mask)return;
document.body.removeChild(mask);