Javascript for simple marquee effect

marquee.js

var w = window,
  d = document,
  e = d.documentElement,
  g = d.getElementsByTagName('body')[0],
  windowX = w.innerWidth || e.clientWidth || g.clientWidth,
  windowY = w.innerHeight|| e.clientHeight|| g.clientHeight;

function cumulativeOffsetLeft(el) {
  var left = 0;

  while (el) {
    left += el.offsetLeft || 0;
    el = el.offsetParent;
  }

  return left;
}

function marquee(el, options) {
  options = options || {};
  var dir = options.dir || 'right';
  var relativeToParent = options.relativeToParent || false;
  var step = dir === 'left' ? -2 : 2;
  var offsetWidth = el.offsetWidth;
  var offsetLeft, outerWidth;
  el.style.position = "relative";

  if (relativeToParent) {
    el.parentNode.style.overflow = "hidden";
    offsetLeft = 0;
    outerWidth = el.parentNode.offsetWidth;
  } else {
    offsetLeft = cumulativeOffsetLeft(el);
    outerWidth = windowX;
  }

  window.setInterval(function() {
    var left = parseInt(el.style.left) || 0;
    left = left + step;
    var cond = dir === 'left' ? (left + offsetLeft + offsetWidth < 0) : (left + offsetLeft > outerWidth);
    if (cond) { left = 0; }
    el.style.left = left + "px";
  }, 10);
}