add scroll selector

src/ui/component/router/index.js

@@ -1,10 +1,9 @@
 import { connect } from 'react-redux';
+import { selectScrollStartingPosition } from 'redux/selectors/app';
 import Router from './view';
 
 const select = state => ({
-  scroll: state.app.scrollHistory[state.app.scrollHistory.length - 1],
-  scrollHistory: state.app.scrollHistory,
-  currentScroll: state.app.currentScroll || 0,
+  currentScroll: selectScrollStartingPosition(state),
 });
 
 export default connect(select)(Router);

src/ui/component/router/view.jsx

@@ -22,7 +22,7 @@ import NavigationHistory from 'page/navigationHistory';
 import TagsPage from 'page/tags';
 import FollowingPage from 'page/following';
 
-// Let app handle scroll
+// Tell the browser we are handling scroll restoration
 if ('scrollRestoration' in history) {
   history.scrollRestoration = 'manual';
 }

src/ui/redux/reducers/app.js

@@ -67,6 +67,8 @@ const defaultState: AppState = {
   scrollHistory: [0],
 };
 
+// @@router comes from react-router
+// This action is dispatched any time a user navigates forward or back
 reducers['@@router/LOCATION_CHANGE'] = (state, action) => {
   const { currentScroll } = state;
   const scrollHistory = state.scrollHistory.slice();

src/ui/redux/selectors/app.js

@@ -123,3 +123,8 @@ export const selectSearchOptionsExpanded = createSelector(
   selectState,
   state => state.searchOptionsExpanded
 );
+
+export const selectScrollStartingPosition = createSelector(
+  selectState,
+  state => state.currentScroll
+);