[fixed] Window scrolling

The router now remembers the last window scroll position at various
paths and automatically scrolls the window to match after transitions
complete unless preserveScrollPosition=true is used.

This commit also introduces a flux-style architecture to the high-level
transitionTo/replaceWith/goBack methods.

Fixes remix-run#189
Fixes remix-run#186

Author: mjackson

goBack.js

@@ -1 +1 @@
-module.exports = require('./modules/helpers/goBack');
+module.exports = require('./modules/actions/LocationActions').goBack;

modules/actions/LocationActions.js

@@ -0,0 +1,57 @@
+var LocationDispatcher = require('../dispatchers/LocationDispatcher');
+var makePath = require('../helpers/makePath');
+
+/**
+ * Actions that modify the URL.
+ */
+var LocationActions = {
+
+  PUSH: 'push',
+  REPLACE: 'replace',
+  POP: 'pop',
+  UPDATE_SCROLL: 'update-scroll',
+
+  /**
+   * Transitions to the URL specified in the arguments by pushing
+   * a new URL onto the history stack.
+   */
+  transitionTo: function (to, params, query) {
+    LocationDispatcher.handleViewAction({
+      type: LocationActions.PUSH,
+      path: makePath(to, params, query)
+    });
+  },
+
+  /**
+   * Transitions to the URL specified in the arguments by replacing
+   * the current URL in the history stack.
+   */
+  replaceWith: function (to, params, query) {
+    LocationDispatcher.handleViewAction({
+      type: LocationActions.REPLACE,
+      path: makePath(to, params, query)
+    });
+  },
+
+  /**
+   * Transitions to the previous URL.
+   */
+  goBack: function () {
+    LocationDispatcher.handleViewAction({
+      type: LocationActions.POP
+    });
+  },
+
+  /**
+   * Updates the window's scroll position to the last known position
+   * for the current URL path.
+   */
+  updateScroll: function () {
+    LocationDispatcher.handleViewAction({
+      type: LocationActions.UPDATE_SCROLL
+    });
+  }
+
+};
+
+module.exports = LocationActions;

modules/components/Link.js

@@ -1,7 +1,7 @@
 var React = require('react');
 var ActiveState = require('../mixins/ActiveState');
+var transitionTo = require('../actions/LocationActions').transitionTo;
 var withoutProperties = require('../helpers/withoutProperties');
-var transitionTo = require('../helpers/transitionTo');
 var hasOwnProperty = require('../helpers/hasOwnProperty');
 var makeHref = require('../helpers/makeHref');
 var warning = require('react/lib/warning');

modules/components/Routes.js

@@ -2,9 +2,8 @@ var React = require('react');
 var warning = require('react/lib/warning');
 var copyProperties = require('react/lib/copyProperties');
 var Promise = require('es6-promise').Promise;
+var LocationActions = require('../actions/LocationActions');
 var Route = require('../components/Route');
-var goBack = require('../helpers/goBack');
-var replaceWith = require('../helpers/replaceWith');
 var Path = require('../helpers/Path');
 var Redirect = require('../helpers/Redirect');
 var Transition = require('../helpers/Transition');
@@ -37,9 +36,9 @@ function defaultAbortedTransitionHandler(transition) {
   var reason = transition.abortReason;
 
   if (reason instanceof Redirect) {
-    replaceWith(reason.to, reason.params, reason.query);
+    LocationActions.replaceWith(reason.to, reason.params, reason.query);
   } else {
-    goBack();
+    LocationActions.goBack();
   }
 }
 
@@ -59,6 +58,11 @@ function defaultTransitionErrorHandler(error) {
   throw error; // This error probably originated in a transition hook.
 }
 
+function maybeUpdateScroll(routes, rootRoute) {
+  if (!routes.props.preserveScrollPosition && !rootRoute.props.preserveScrollPosition)
+    LocationActions.updateScroll();
+}
+
 /**
  * The <Routes> component configures the route hierarchy and renders the
  * route matching the current location when rendered into a document.
@@ -98,7 +102,6 @@ var Routes = React.createClass({
     };
   },
 
-
   getLocation: function () {
     var location = this.props.location;
 
@@ -185,7 +188,7 @@ var Routes = React.createClass({
         var rootMatch = getRootMatch(nextState.matches);
 
         if (rootMatch)
-          maybeScrollWindow(routes, rootMatch.route);
+          maybeUpdateScroll(routes, rootMatch.route);
       }
 
       return transition;
@@ -443,11 +446,4 @@ function reversedArray(array) {
   return array.slice(0).reverse();
 }
 
-function maybeScrollWindow(routes, rootRoute) {
-  if (routes.props.preserveScrollPosition || rootRoute.props.preserveScrollPosition)
-    return;
-
-  window.scrollTo(0, 0);
-}
-
 module.exports = Routes;

modules/dispatchers/LocationDispatcher.js

@@ -0,0 +1,18 @@
+var copyProperties = require('react/lib/copyProperties');
+var Dispatcher = require('react-dispatcher');
+
+/**
+ * Dispatches actions that modify the URL.
+ */
+var LocationDispatcher = copyProperties(new Dispatcher, {
+
+  handleViewAction: function (action) {
+    this.dispatch({
+      source: 'VIEW_ACTION',
+      action: action
+    });
+  }
+
+});
+
+module.exports = LocationDispatcher;

modules/helpers/Transition.js

@@ -1,5 +1,5 @@
 var mixInto = require('react/lib/mixInto');
-var transitionTo = require('./transitionTo');
+var transitionTo = require('../actions/LocationActions').transitionTo;
 var Redirect = require('./Redirect');
 
 /**

modules/helpers/goBack.js

@@ -1,5 +1,7 @@
 var warning = require('react/lib/warning');
 var EventEmitter = require('events').EventEmitter;
+var LocationActions = require('../actions/LocationActions');
+var LocationDispatcher = require('../dispatchers/LocationDispatcher');
 var supportsHistory = require('../helpers/supportsHistory');
 var HistoryLocation = require('../locations/HistoryLocation');
 var RefreshLocation = require('../locations/RefreshLocation');
@@ -11,6 +13,15 @@ function notifyChange() {
   _events.emit(CHANGE_EVENT);
 }
 
+var _scrollPositions = {};
+
+function recordScrollPosition(path) {
+  _scrollPositions[path] = {
+    x: window.scrollX,
+    y: window.scrollY
+  };
+}
+
 var _location;
 
 /**
@@ -58,27 +69,57 @@ var PathStore = {
     _location = null;
   },
 
+  /**
+   * Returns the location object currently in use.
+   */
   getLocation: function () {
     return _location;
   },
 
-  push: function (path) {
-    if (_location.getCurrentPath() !== path)
-      _location.push(path);
-  },
-
-  replace: function (path) {
-    if (_location.getCurrentPath() !== path)
-      _location.replace(path);
+  /**
+   * Returns the current URL path.
+   */
+  getCurrentPath: function () {
+    return _location.getCurrentPath();
   },
 
-  pop: function () {
-    _location.pop();
+  /**
+   * Returns the last known scroll position for the given path.
+   */
+  getScrollPosition: function (path) {
+    return _scrollPositions[path] || { x: 0, y: 0 };
   },
 
-  getCurrentPath: function () {
-    return _location.getCurrentPath();
-  }
+  dispatchToken: LocationDispatcher.register(function (payload) {
+    var action = payload.action;
+    var currentPath = _location.getCurrentPath();
+
+    switch (action.type) {
+      case LocationActions.PUSH:
+        if (currentPath !== action.path) {
+          recordScrollPosition(currentPath);
+          _location.push(action.path);
+        }
+        break;
+
+      case LocationActions.REPLACE:
+        if (currentPath !== action.path) {
+          recordScrollPosition(currentPath);
+          _location.replace(action.path);
+        }
+        break;
+
+      case LocationActions.POP:
+        recordScrollPosition(currentPath);
+        _location.pop();
+        break;
+
+      case LocationActions.UPDATE_SCROLL:
+        var p = PathStore.getScrollPosition(currentPath);
+        window.scrollTo(p.x, p.y);
+        break;
+    }
+  })
 
 };