code: function _whichTransitionEndEvent() {
      var t;
      var el = document.createElement("fakeelement");
      var transitions = {
        "WebkitTransition": "webkitTransitionEnd",
        "MozTransition": "transitionend",
        "MSTransition": "msTransitionEnd",
        "OTransition": "otransitionend",
        "transition": "transitionend",
      };
      for (t in transitions) {
        if (transitions.hasOwnProperty(t)) {
          if (el.style[t] !== undefined) {
            return transitions[t];
          }
        }
      }
    }
docs: Find the CSS transition end event that we should listen for.
  
  @returns {string} t - the transition string