window.addEventListener( 'load', function() {
var logo = document.getElementById('logo'),
docHeight = document.documentElement.offsetHeight;
window.addEventListener( 'scroll', function() {
// normalize scroll position as percentage
var scrolled = window.scrollY / ( docHeight - window.innerHeight ),
transformValue = 'scale('+scrolled+')';
logo.style.WebkitTransform = transformValue;
logo.style.MozTransform = transformValue;
logo.style.OTransform = transformValue;
logo.style.transform = transformValue;
}, false);
}, false); 
