polyfill for detecting AnimationEnd and TransitionEnd event - from ReactTransitionEvents.js

detectAnimationEnd.js

/**
 * EVENT_NAME_MAP is used to determine which event fired when a
 * transition/animation ends, based on the style property used to
 * define that event.
 */
var EVENT_NAME_MAP = {
  transitionend: {
    'transition': 'transitionend',
    'WebkitTransition': 'webkitTransitionEnd',
    'MozTransition': 'mozTransitionEnd',
    'OTransition': 'oTransitionEnd',
    'msTransition': 'MSTransitionEnd'
  },

  animationend: {
    'animation': 'animationend',
    'WebkitAnimation': 'webkitAnimationEnd',
    'MozAnimation': 'mozAnimationEnd',
    'OAnimation': 'oAnimationEnd',
    'msAnimation': 'MSAnimationEnd'
  }
};

var endEvents = [];

function detectEvents() {
  var testEl = document.createElement('div');
  var style = testEl.style;

  // On some platforms, in particular some releases of Android 4.x,
  // the un-prefixed "animation" and "transition" properties are defined on the
  // style object but the events that fire will still be prefixed, so we need
  // to check if the un-prefixed events are useable, and if not remove them
  // from the map
  if (!('AnimationEvent' in window)) {
    delete EVENT_NAME_MAP.animationend.animation;
  }

  if (!('TransitionEvent' in window)) {
    delete EVENT_NAME_MAP.transitionend.transition;
  }

  for (var baseEventName in EVENT_NAME_MAP) {
    var baseEvents = EVENT_NAME_MAP[baseEventName];
    for (var styleName in baseEvents) {
      if (styleName in style) {
        endEvents.push(baseEvents[styleName]);
        break;
      }
    }
  }
}