block7.js

if (this.props.viewabilityConfigCallbackPairs) {
      this._viewabilityTuples = this.props.viewabilityConfigCallbackPairs.map(
        pair => ({
          viewabilityHelper: new ViewabilityHelper(pair.viewabilityConfig),
          onViewableItemsChanged: pair.onViewableItemsChanged,
        }),
      );
    } else if (this.props.onViewableItemsChanged) {
      this._viewabilityTuples.push({
        viewabilityHelper: new ViewabilityHelper(this.props.viewabilityConfig),
        onViewableItemsChanged: this.props.onViewableItemsChanged,
      });
    }