javascript弹出层居中，js的Window size and scrolling

有一个文章的帮助很大：
http://www.howtocreate.co.uk/tutorials/javascript/browserwindow这个文章介绍取得当前浏览器长宽的办法，还有当前浏览器的scroll偏移的xy值，这样，我们就可以定位一个层在页面中间了

窗口长宽的代码

function getInnerXY() {
  var myWidth = 0, myHeight = 0;
  if( typeof( window.innerWidth ) == 'number' ) {
    //Non-IE
    myWidth = window.innerWidth;
    myHeight = window.innerHeight;
  } else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) {
    //IE 6+ in 'standards compliant mode'
    myWidth = document.documentElement.clientWidth;
    myHeight = document.documentElement.clientHeight;
  } else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
    //IE 4 compatible
    myWidth = document.body.clientWidth;
    myHeight = document.body.clientHeight;
  }
  return [myWidth, myHeight];
}

scroller偏移的代码

function getScrollXY() {
  var scrOfX = 0, scrOfY = 0;
  if( typeof( window.pageYOffset ) == 'number' ) {
    //Netscape compliant
    scrOfY = window.pageYOffset;
    scrOfX = window.pageXOffset;
  } else if( document.body && ( document.body.scrollLeft || document.body.scrollTop ) ) {
    //DOM compliant
    scrOfY = document.body.scrollTop;
    scrOfX = document.body.scrollLeft;
  } else if( document.documentElement && ( document.documentElement.scrollLeft || document.documentElement.scrollTop ) ) {
    //IE6 standards compliant mode
    scrOfY = document.documentElement.scrollTop;
    scrOfX = document.documentElement.scrollLeft;
  }
  return [ scrOfX, scrOfY ];
}

下面是让层居中，注意，ie的行为不一致，导致要单独判断是否加上偏移:
function showDialog (did) {
??? G("blankiframe").style.display = "block";
??? G("bmask").style.display="block";
??? var el = G(did);
??? el.style.display = "block";

??? var innerxy = getInnerXY();
??? // add the offset
??? var offxy = getScrollXY();
??? if (js.util.browser.msie) { // ie
??? ??? el.style.top = ((innerxy[1]-el.clientHeight)/2 + offxy[1])+"px";
??? ??? el.style.left = ((innerxy[0]-el.clientWidth)/2 + offxy[0])+"px";
??? } else {
??? ??? el.style.top = ((innerxy[1]-el.clientHeight)/2)+"px";
??????? el.style.left = ((innerxy[0]-el.clientWidth)/2)+"px";
??? }
???
//??? el.style.marginTop = -(el.clientHeight/2) + "px";
//??? el.style.marginLeft = "-240px";
}

加上一下js.util.browser的代码：
var userAgent = navigator.userAgent.toLowerCase();
// Figure out what browser is being used
js.util.browser = {
??? version: (userAgent.match(/.+(?:rv|it|ra|ie)[\/: ]([\d.]+)/) || [])[1],
??? safari: /webkit/.test(userAgent) && !/chrome/.test(userAgent),
??? chrome: /chrome/.test(userAgent),
??? opera: /opera/.test(userAgent),
??? msie: /msie/.test(userAgent) && !/opera/.test(userAgent),
??? mozilla: /mozilla/.test(userAgent) && !/(compatible|webkit)/.test(userAgent)
};