simple javascript parallax script

parallax

// Create cross browser requestAnimationFrame method:
window.requestAnimationFrame = window.requestAnimationFrame
 || window.mozRequestAnimationFrame
 || window.webkitRequestAnimationFrame
 || window.msRequestAnimationFrame
 || function(f){setTimeout(f, 1000/60)}

var parallaxElem = document.getElementById('parallax-content');
var scrollRate = .5; // move parallaxElem at 50% of scroll rate

function parallaxThis() {
  var scrolltop = window.pageYOffset;
  parallaxElem.style.marginTop = (-scrolltop * scrollRate) + 'px';
};

window.addEventListener('scroll', function() {
  requestAnimationFrame(parallaxThis);
}, false);