Function getNativeBeforeInputChars

docs/external/js/react-dom.development.js:8969–9014

* @param {TopLevelType} topLevelType Number from `TopLevelType`. * @param {object} nativeEvent Native browser event. * @return {?string} The string corresponding to this `beforeInput` event.

(topLevelType, nativeEvent)

  function getNativeBeforeInputChars(topLevelType, nativeEvent) {
    switch (topLevelType) {
      case TOP_COMPOSITION_END:
        return getDataFromCustomEvent(nativeEvent);

      case TOP_KEY_PRESS:
        /**
         * If native `textInput` events are available, our goal is to make
         * use of them. However, there is a special case: the spacebar key.
         * In Webkit, preventing default on a spacebar `textInput` event
         * cancels character insertion, but it *also* causes the browser
         * to fall back to its default spacebar behavior of scrolling the
         * page.
         *
         * Tracking at:
         * https://code.google.com/p/chromium/issues/detail?id=355103
         *
         * To avoid this issue, use the keypress event as if no `textInput`
         * event is available.
         */
        var which = nativeEvent.which;

        if (which !== SPACEBAR_CODE) {
          return null;
        }

        hasSpaceKeypress = true;
        return SPACEBAR_CHAR;

      case TOP_TEXT_INPUT:
        // Record the characters to be added to the DOM.
        var chars = nativeEvent.data; // If it's a spacebar character, assume that we have already handled
        // it at the keypress level and bail immediately. Android Chrome
        // doesn't give us keycodes, so we need to ignore it.

        if (chars === SPACEBAR_CHAR && hasSpaceKeypress) {
          return null;
        }

        return chars;

      default:
        // For other native event types, do nothing.
        return null;
    }
  }
  /**
   * For browsers that do not provide the `textInput` event, extract the
   * appropriate string to use for SyntheticInputEvent.