Centrer Div avec javascript

function centerMe(myDiv)
 {

    var arrayPageSize = getPageSize();
    var object2 = document.getElementById(myDiv);
 object2.style.top=((arrayPageSize[3]/2) - (object2.offsetWidth / 2))+'px';
 object2.style.left=((arrayPageSize[2]/2) -(object2.offsetHeight / 2)) +'px';
       
 }
 function getPageSize(){
 
 var xScroll, yScroll;
 
 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;
 }
 
 var windowWidth, windowHeight;
 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;
 }

 arrayPageSize = new Array(pageWidth,pageHeight,windowWidth,windowHeight)
 return arrayPageSize;
}