fix(previous): Previous state no longer tracks abstract from-states (…

…e.g., root)

 Closes #123

src/previous.js

@@ -4,8 +4,14 @@ angular.module('ct.ui.router.extras.previous', [ 'ct.ui.router.extras.core', 'ct
       var previous = null, lastPrevious = null, memos = {};
 
       $rootScope.$on("$transitionStart", function(evt, $transition$) {
-        lastPrevious = previous;
-        previous = $transition$.from;
+        var from = $transition$.from;
+        // Check if the fromState is navigable before tracking it.
+        // Root state doesn't get decorated with $$state().  Doh.
+        var fromState = from.state && from.state.$$state && from.state.$$state();
+        if (fromState && fromState.navigable) {
+          lastPrevious = previous;
+          previous = $transition$.from;
+        }
 
         $transition$.promise.then(commit).catch(revert);
         function commit() { lastPrevious = null; }

test/previousSpec.js

@@ -53,26 +53,36 @@ describe("$previousState", function () {
     $previousState = $get('$previousState');
   }));
 
+  // Test for #123
+  it("should not capture root state (or non-navigable states)", inject(function($rootScope) {
+    testGo("top", { entered: 'top' });
+    expect($previousState.get()).toBeNull();
+  }));
+
+
   describe('.go()', function () {
     it("should transition back to the previous state", function () {
       testGo("top.people.managerlist", { entered: pathFrom('top', 'top.people.managerlist') });
-      testGo("top.inv.storelist", { entered: pathFrom('top.inv', 'top.inv.storelist') , exited: pathFrom('top.people.managerlist', 'top.people') });
+      testGo("top.inv.storelist", { entered: pathFrom('top.inv', 'top.inv.storelist'), exited: pathFrom('top.people.managerlist', 'top.people') });
       $previousState.go();
       $q.flush();
       expect($state.current.name === "tabs.tabs2");
     });
+  });
 
+  describe('.get()', function() {
     // Test for #120
-    it("should go to previous state after another transition is cancelled", inject(function($rootScope) {
+    it("should not return current state, after a transition is cancelled", inject(function($rootScope) {
       testGo("top", { entered: 'top' });
       testGo("top.people.managerlist", { entered: ['top.people', 'top.people.managerlist'] });
 
       var transitionNum = 0;
       $rootScope.$on("$stateChangeStart", function(evt) { if (transitionNum++ === 0) { evt.preventDefault(); } });
 
       testGo("top.inv.storelist", undefined, { redirect: 'top.people.managerlist'}); // Cancelled, so we're still at original state
+
       expect($previousState.get().state.name).toBe("top");
-    }));
+    }))
   });
 
   describe('.memo()', function () {