Function extractCompositionEvent

docs/external/js/react-dom.development.js:8915–8961

* @return {?object} A SyntheticCompositionEvent.

(topLevelType, targetInst, nativeEvent, nativeEventTarget)

   */

  function extractCompositionEvent(topLevelType, targetInst, nativeEvent, nativeEventTarget) {
    var eventType;
    var fallbackData;

    if (canUseCompositionEvent) {
      eventType = getCompositionEventType(topLevelType);
    } else if (!isComposing) {
      if (isFallbackCompositionStart(topLevelType, nativeEvent)) {
        eventType = eventTypes.compositionStart;
      }
    } else if (isFallbackCompositionEnd(topLevelType, nativeEvent)) {
      eventType = eventTypes.compositionEnd;
    }

    if (!eventType) {
      return null;
    }

    if (useFallbackCompositionData && !isUsingKoreanIME(nativeEvent)) {
      // The current composition is stored statically and must not be
      // overwritten while composition continues.
      if (!isComposing && eventType === eventTypes.compositionStart) {
        isComposing = initialize(nativeEventTarget);
      } else if (eventType === eventTypes.compositionEnd) {
        if (isComposing) {
          fallbackData = getData();
        }
      }
    }

    var event = SyntheticCompositionEvent.getPooled(eventType, targetInst, nativeEvent, nativeEventTarget);

    if (fallbackData) {
      // Inject data generated from fallback path into the synthetic event.
      // This matches the property of native CompositionEventInterface.
      event.data = fallbackData;
    } else {
      var customData = getDataFromCustomEvent(nativeEvent);

      if (customData !== null) {
        event.data = customData;
      }
    }

    accumulateTwoPhaseDispatches(event);
    return event;
  }
  /**
   * @param {TopLevelType} topLevelType Number from `TopLevelType`.
   * @param {object} nativeEvent Native browser event.