feat($state): expose previous state/params via $state

src/state.js

@@ -527,6 +527,9 @@ function $StateProvider(   $urlRouterProvider,   $urlMatcherFactory) {
    * you'd like to test against the current active state.
    * @property {object} current A reference to the state's config object. However 
    * you passed it in. Useful for accessing custom data.
+   * @property {object} previous A reference to the previous state's config object.
+   * @property {object} previousParams A param object, e.g. {sectionId: section.id)}, 
+   * represents the param's of the previous state.
    * @property {object} transition Currently pending transition. A promise that'll 
    * resolve or reject.
    *
@@ -615,6 +618,9 @@ function $StateProvider(   $urlRouterProvider,   $urlMatcherFactory) {
       params: {},
       current: root.self,
       $current: root,
+      previous: root.self,
+      $previous: root,
+      previousParams: {},
       transition: null
     };
 
@@ -900,6 +906,9 @@ function $StateProvider(   $urlRouterProvider,   $urlMatcherFactory) {
         $state.$current = to;
         $state.current = to.self;
         $state.params = toParams;
+        $state.$previous = from;
+        $state.previous = from.self;
+        $state.previousParams = fromParams;
         copy($state.params, $stateParams);
         $state.transition = null;
 

test/stateSpec.js

@@ -586,6 +586,20 @@ describe('state', function () {
   });
 
 
+  describe('.previous', function () {
+    it('is always defined', inject(function ($state) {
+      expect($state.previous).toBeDefined();
+    }));
+
+    it('updates asynchronously as the transitionTo() promise is resolved', inject(function ($state, $q) {
+      initStateTo(A);
+      var trans = $state.transitionTo(B, {});
+      $q.flush();
+      expect($state.previous).toBe(A);
+    }));
+  });
+
+
   describe('$current', function () {
     it('is always defined', inject(function ($state) {
       expect($state.$current).toBeDefined();
@@ -598,6 +612,20 @@ describe('state', function () {
   });
 
 
+  describe('$previous', function () {
+    it('is always defined', inject(function ($state) {
+      expect($state.$previous).toBeDefined();
+    }));
+
+    it('wraps the raw state object', inject(function ($state, $q) {
+      initStateTo(A);
+      var trans = $state.transitionTo(B, {});
+      $q.flush();
+      expect($state.$previous.data).toBe(A.data); // 'data' is reserved for app use
+    }));
+  });
+
+
   describe('.params', function () {
     it('is always defined', inject(function ($state) {
       expect($state.params).toBeDefined();
@@ -611,6 +639,21 @@ describe('state', function () {
   });
 
 
+  describe('.previousParams', function () {
+    it('is always defined', inject(function ($state) {
+      expect($state.previousParams).toBeDefined();
+      expect(angular.isObject($state.previousParams)).toBe(true);
+    }));
+
+    it('contains the parameter values for the previous state', inject(function ($state, $q) {
+      initStateTo(D, { x: 'x value', z: 'invalid value' });
+      var trans = $state.transitionTo(A, {});
+      $q.flush();
+      expect($state.previousParams).toEqual({ x: 'x value', y: undefined });
+    }));
+  });
+
+
   describe('.transition', function () {
     it('is null when no transition is taking place', inject(function ($state, $q) {
       expect($state.transition).toBeNull();