event_pagexy.js

// From jQuery source

// Calculate pageX/Y if missing and clientX/Y available
if ( event.pageX == null && event.clientX != null ) {
  var doc = document.documentElement, body = document.body;
  event.pageX = event.clientX + (doc && doc.scrollLeft || body && body.scrollLeft || 0) - (doc && doc.clientLeft || body && body.clientLeft || 0);
  event.pageY = event.clientY + (doc && doc.scrollTop  || body && body.scrollTop  || 0) - (doc && doc.clientTop  || body && body.clientTop  || 0);
}