javascript实现的弹出层背景置灰-模拟(easyui dialog)

<title>模仿easyui dialog的效果</title>
<script>
//取得页面元素
var getElement = function() {
return document.getElementById(arguments[0]) || false;
}
function openDialog(dialogId) {
var maskId = "mask";
//如果有，先删除原来的
if (getElement(dialogId)) {
document.removeChild(getElement(dialogId));//删除操作：弹出的div
}
if (getElement(maskId)) {
document.removeChild(getElement(maskId));//删除操作：弹出的不可操作(面具)层
}

//背景置灰
var maskDiv = document.createElement("div");
maskDiv.id = maskId;
maskDiv.style.position = "absolute";
maskDiv.style.zIndex = "1";
maskDiv.style.width = document.body.scrollWidth + "px";
maskDiv.style.height = document.body.scrollHeight + "px";
maskDiv.style.top = "0px";
maskDiv.style.left = "0px";
maskDiv.style.background = "gray";
maskDiv.style.filter = "alpha(opacity=10)";
maskDiv.style.opacity = "0.30";//透明度
document.body.appendChild(maskDiv);//向body之中增加背景层

//Dialog
var dialogDiv = document.createElement("div");
dialogDiv.id = dialogId;
dialogDiv.style.position = "absolute";
dialogDiv.style.zIndex = "9999";
dialogDiv.style.width = "400px";
dialogDiv.style.height = "200px";
dialogDiv.style.top = (parseInt(document.body.scrollHeight) - 200) / 2 + "px"; // 屏幕居中
dialogDiv.style.left = (parseInt(document.body.scrollWidth) - 400) / 2 + "px"; // 屏幕居中
dialogDiv.style.background = "white";
dialogDiv.style.border = "1px solid gray";
dialogDiv.style.padding = "5px";
dialogDiv.innerHTML = "(Dialog Content)";
//Dialog之中的关闭操作：关闭背景层和Dialog层
var closeControlloer = document.createElement("a");//创建一个超链接(做为关闭的触发)
closeControlloer.href = "#";
closeControlloer.innerHTML = "关闭";
closeControlloer.onclick = function() {
document.body.removeChild(getElement(dialogId));//删除diaglog
document.body.removeChild(getElement(maskId));//删除背景层
}
dialogDiv.appendChild(closeControlloer);//dialog之中增加"关闭"操作
document.body.appendChild(dialogDiv);//body之中增加dialog
}
</script>
<a href="#" onclick="openDialog('dialog');">Open Dialog</a>