Function getFallbackBeforeInputChars

docs/lib/react.js:316–360

* For browsers that do not provide the `textInput` event, extract the * appropriate string to use for SyntheticInputEvent. * * @param {string} topLevelType Record from `EventConstants`. * @param {object} nativeEvent Native browser event. * @return {?string} The fallback string for this `beforeI

(topLevelType, nativeEvent)

 * @return {?string} The fallback string for this `beforeInput` event.
 */
function getFallbackBeforeInputChars(topLevelType, nativeEvent) {
  // If we are currently composing (IME) and using a fallback to do so,
  // try to extract the composed characters from the fallback object.
  if (currentComposition) {
    if (topLevelType === topLevelTypes.topCompositionEnd || isFallbackCompositionEnd(topLevelType, nativeEvent)) {
      var chars = currentComposition.getData();
      FallbackCompositionState.release(currentComposition);
      currentComposition = null;
      return chars;
    }
    return null;
  }

  switch (topLevelType) {
    case topLevelTypes.topPaste:
      // If a paste event occurs after a keypress, throw out the input
      // chars. Paste events should not lead to BeforeInput events.
      return null;
    case topLevelTypes.topKeyPress:
      /**
       * As of v27, Firefox may fire keypress events even when no character
       * will be inserted. A few possibilities:
       *
       * - `which` is `0`. Arrow keys, Esc key, etc.
       *
       * - `which` is the pressed key code, but no char is available.
       *   Ex: 'AltGr + d` in Polish. There is no modified character for
       *   this key combination and no character is inserted into the
       *   document, but FF fires the keypress for char code `100` anyway.
       *   No `input` event will occur.
       *
       * - `which` is the pressed key code, but a command combination is
       *   being used. Ex: `Cmd+C`. No character is inserted, and no
       *   `input` event will occur.
       */
      if (nativeEvent.which && !isKeypressCommand(nativeEvent)) {
        return String.fromCharCode(nativeEvent.which);
      }
      return null;
    case topLevelTypes.topCompositionEnd:
      return useFallbackCompositionData ? null : nativeEvent.data;
    default:
      return null;
  }
}

/**
 * Extract a SyntheticInputEvent for `beforeInput`, based on either native