pageWidth = 0;
pageHeight = 0;
function getWindow(){
  pageWidth =  window.innerWidth;
  pageWidth = (pageWidth)? pageWidth : document.documentElement.clientWidth;
  pageWidth = (pageWidth)? pageWidth: document.body.clientWidth;
  pageHeight =  window.innerHeight;
  pageHeight = (pageHeight)? pageHeight: document.documentElement.clientHeight;
  pageHeight = (pageHeight)? pageHeight: document.body.clientHeight;
}

function posDiv(){
  getWindow();
  // var myDiv = $('global');
  var myDiv = document.getElementById("global");
  var posLeft = (pageWidth-myDiv.offsetWidth)/2;
  myDiv.style.left = (posLeft<0)?0+"px":posLeft+"px";
  var posTop = (pageHeight-myDiv.offsetHeight)/2;
  myDiv.style.top = (posTop<0)?0+"px":posTop+"px";
}