js重写alert样式

window.alert = function(txt)
{
var winSize = function(){
var xScroll, yScroll, windowWidth, windowHeight, pageWidth, pageHeight;
// innerHeight获取的是可视窗口的高度，IE不支持此属性
if (window.innerHeight && window.scrollMaxY) {
xScroll = document.body.scrollWidth;
yScroll = window.innerHeight + window.scrollMaxY;
} else if (document.body.scrollHeight > document.body.offsetHeight) { // all but Explorer Mac
xScroll = document.body.scrollWidth;
yScroll = document.body.scrollHeight;
} else { // Explorer Mac...would also work in Explorer 6 Strict, Mozilla and Safari
xScroll = document.body.offsetWidth;
yScroll = document.body.offsetHeight;
}

if (self.innerHeight) {    // all except Explorer
windowWidth = self.innerWidth;
windowHeight = self.innerHeight;
} else if (document.documentElement && document.documentElement.clientHeight) { // Explorer 6 Strict Mode
windowWidth = document.documentElement.clientWidth;
windowHeight = document.documentElement.clientHeight;
} else if (document.body) { // other Explorers
windowWidth = document.body.clientWidth;
windowHeight = document.body.clientHeight;
}

// for small pages with total height less then height of the viewport
if (yScroll < windowHeight) {
pageHeight = windowHeight;
} else {
pageHeight = yScroll;
}

// for small pages with total width less then width of the viewport
if (xScroll < windowWidth) {
pageWidth = windowWidth;
} else {
pageWidth = xScroll;
}

return{
'pageWidth':pageWidth,
'pageHeight':pageHeight,
'windowWidth':windowWidth,
'windowHeight':windowHeight
}
}();

var shield = document.createElement("DIV");
shield.id = "shield";
shield.style.position = "absolute";
shield.style.left = "0px";
shield.style.top = "0px";
shield.style.width =  winSize.pageWidth+"px";
shield.style.height = document.body.scrollHeight+"px";
shield.style.background = "rgba(51,51,51,0.6)";
shield.style.textAlign = "center";
shield.style.zIndex = "10000";
shield.style.filter = "alpha(opacity=0)";
var alertFram = document.createElement("DIV");
alertFram.id="alertFram";
alertFram.style.position = "fixed";
alertFram.style.left = "15%";
alertFram.style.top = (winSize.windowHeight / 2 - 150)+"px";
alertFram.style.width =  "70%";
alertFram.style.height = "150px";
alertFram.style.background = "#ccc";
alertFram.style.textAlign = "center";
alertFram.style.lineHeight = "150px";
alertFram.style.zIndex = "10001";
strHtml = "<ul style=\"list-style:none;margin:0px;padding:0px;width:100%\">\n";
strHtml += " <li style=\"background:#fff;text-align:left;padding-left:10px;font-size:14px;height:25px;line-height:25px;border-bottom:1px solid #ff6a01;\">[系统提示]</li>\n";
strHtml += " <li style=\"background:#fff;text-align:center;font-size:14px;height:120px;line-height:120px;\">"+txt+"</li>\n";
strHtml += " <li style=\"background:#fff;text-align:center;font-weight:bold;height:28px;line-height:28px; border-top:1px solid #ff6a01;\"><input style=\"background:#fff;color:#000;font-size:14px;height:27px;line-height:27px;\" type=\"button\" value=\"确 定\" onclick=\"doOk()\" /></li>\n";
strHtml += "</ul>\n";
alertFram.innerHTML = strHtml;
document.body.appendChild(alertFram);
document.body.appendChild(shield);
var c = 0;
this.doAlpha = function(){
if (c++ > 20){clearInterval(ad);return 0;}
shield.style.filter = "alpha(opacity="+c+");";
}
var ad = setInterval("doAlpha()",5);
this.doOk = function(){
alertFram.style.display = "none";
shield.style.display = "none";
}
alertFram.focus();
document.body.onselectstart = function(){return false;};
}