text: var s = document.body || document.documentElement, s = s.style;
  var prefixTransition = '';
  
  if (s.WebkitTransition === '') prefixTransition = '-webkit-';
  if (s.MozTransition === '') prefixTransition = '-moz-';
  if (s.OTransition === '') prefixTransition = '-o-';
  
  module.exports = function(el, callback) {
      var runOnce = function runOnce(e) {
          el.removeEventListener('webkitTransitionEnd', runOnce);
          el.removeEventListener('mozTransitionEnd', runOnce);
          el.removeEventListener('oTransitionEnd', runOnce);
          el.removeEventListener('transitionend', runOnce);
          el.removeEventListener('transitionend', runOnce);
          callback();
      };
  
      el.addEventListener('webkitTransitionEnd', runOnce);
      el.addEventListener('mozTransitionEnd', runOnce);
      el.addEventListener('oTransitionEnd', runOnce);
      el.addEventListener('transitionend', runOnce);
      el.addEventListener('transitionend', runOnce);
  
      if (prefixTransition === '' && !('transition' in s)) {
          callback();
      }
  };
  