gistfile1.js

var width = null;
var height = null;

window.onload = function () {
  var windowSize = getSize();
  width = windowSize['width'];
  height = windowSize['height'];
  window.onscroll = function(){ alert("Hello"); }
};

function getSize () {
  var winW = 630, winH = 460;
  if (document.body && document.body.offsetWidth) {
    winW = document.body.offsetWidth;
    winH = document.body.offsetHeight;
  }
  if (document.compatMode=='CSS1Compat' &&
      document.documentElement &&
      document.documentElement.offsetWidth ) {
    winW = document.documentElement.offsetWidth;
    winH = document.documentElement.offsetHeight;
  }
  if (window.innerWidth && window.innerHeight) {
    winW = window.innerWidth;
    winH = window.innerHeight;
  }
  return {
    'width': winW,
    'height': winH
  };