message: Navigated to top of stack in js
diff: @@ -19,6 +19,7 @@ class NavigationStack extends React.Component<NavigationStackProps, NavigationSt
  this.handleBack = this.handleBack.bind(this);
  this.onWillNavigateBack = this.onWillNavigateBack.bind(this);
  this.onDidNavigateBack = this.onDidNavigateBack.bind(this);
  + this.onNavigateToTop = this.onNavigateToTop.bind(this);
  }
  static defaultProps = {
  fragmentMode: true,
  @@ -56,6 +57,12 @@ class NavigationStack extends React.Component<NavigationStackProps, NavigationSt
  if (this.resumeNavigation)
  this.resumeNavigation();
  }
  + onNavigateToTop() {
  + var {stateNavigator} = this.props;
  + var {crumbs} = stateNavigator.stateContext;
  + if (crumbs.length > 0)
  + stateNavigator.navigateBack(crumbs.length);
  + }
  handleBack() {
  var {primary, fragmentMode} = this.props;
  this.setState(() => (!fragmentMode || primary) ? ({finish: true}): null);
  @@ -100,7 +107,8 @@ class NavigationStack extends React.Component<NavigationStackProps, NavigationSt
  style={[styles.stack, fragmentMode ? {backgroundColor: '#000'} : null]}
  {...this.getAnimation()}
  onWillNavigateBack={this.onWillNavigateBack}
  - onDidNavigateBack={this.onDidNavigateBack}>
  + onDidNavigateBack={this.onDidNavigateBack}
  + onNavigateToTop={this.onNavigateToTop}>
  <BackButton onPress={this.handleBack} />
  <PrimaryStackContext.Provider value={false}>
  <PopSync<{crumb: number}>
  