(function() {
   var mousePos;

   document.onmousemove = handleMouseMove;
   setInterval(getMousePosition, 100); // setInterval repeats every X ms

   function handleMouseMove(event) {
       var dot, eventDoc, doc, body, pageX, pageY;

       event = event || window.event; // IE-ism

       // If pageX/Y aren't available and clientX/Y are,
       // calculate pageX/Y - logic taken from jQuery.
       // (This is to support old IE)
       if (event.pageX == null && event.clientX != null) {
           eventDoc = (event.target && event.target.ownerDocument) || document;
           doc = eventDoc.documentElement;
           body = eventDoc.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 );
       }

       mousePos = {
           x: event.pageX,
           y: event.pageY
       };
   }
   function getMousePosition() {
       var pos = mousePos;
       if (!pos) {
           // We haven't seen any movement yet
       }
       else {
           // Use pos.x and pos.y
       }
   }
})();