if (getItemLayout) {
        /* $FlowFixMe[prop-missing] (>=0.63.0 site=react_native_fb) This comment
         * suppresses an error found when Flow v0.63 was deployed. To see the error
         * delete this comment and run Flow. */
        return getItemLayout(data, index);
      }
Gets an approximate offset to an item at a given index. Supports
fractional indices.