code: function whichAnimationEvent() {
    let t;
    let el = document.createElement('fakeelement');
  
    const animations = {
      animation: 'animationend',
      OAnimation: 'oAnimationEnd',
      MozAnimation: 'animationend',
      WebkitAnimation: 'webkitAnimationEnd',
    };
  
    for (t in animations) {
      if (el.style[t] !== undefined) {
        return animations[t];
      }
    }
  }
docs: /* From Modernizr