navbar-step-2.js

[...]

class App extends Component {
  constructor(props) {
    [...]

    const scrollAnim = new Animated.Value(0);
    const offsetAnim = new Animated.Value(0);

    this.state = {
      dataSource: dataSource.cloneWithRows(data),
      scrollAnim,
      offsetAnim,
      clampedScroll: Animated.diffClamp(
        Animated.add(
          scrollAnim.interpolate({
            inputRange: [0, 1],
            outputRange: [0, 1],
            extrapolateLeft: 'clamp',
          }),
          offsetAnim,
        ),
        0,
        NAVBAR_HEIGHT - STATUS_BAR_HEIGHT,
      ),
    };
  }
  [...]
}

[...]