Function extractBeforeInputEvent

code/third-party/public/app.js:2685–2705

* Extract a SyntheticInputEvent for `beforeInput`, based on either native * `textInput` or fallback behavior. * * @return {?object} A SyntheticInputEvent.

(topLevelType, targetInst, nativeEvent, nativeEventTarget)

 * @return {?object} A SyntheticInputEvent.
 */
function extractBeforeInputEvent(topLevelType, targetInst, nativeEvent, nativeEventTarget) {
  var chars = void 0;

  if (canUseTextInputEvent) {
    chars = getNativeBeforeInputChars(topLevelType, nativeEvent);
  } else {
    chars = getFallbackBeforeInputChars(topLevelType, nativeEvent);
  }

  // If no characters are being inserted, no BeforeInput event should
  // be fired.
  if (!chars) {
    return null;
  }

  var event = SyntheticInputEvent.getPooled(eventTypes.beforeInput, targetInst, nativeEvent, nativeEventTarget);

  event.data = chars;
  accumulateTwoPhaseDispatches(event);
  return event;
}

/**
 * Create an `onBeforeInput` event to match