corrected bug when restoring more times than stored

backbone.memento.js

@@ -17,6 +17,13 @@ Backbone.Memento = function(model){
   function getRemovedAttrDiff(newAttrs, oldAttrs){
     var removedAttrs = [];
 
+    // guard clause to ensure we have attrs to compare
+    if (!newAttrs || !oldAttrs){
+      return removedAttrs;
+    }
+
+    // if the attr is found in the old set but not in
+    // the new set, then it was remove in the new set
     for (var attr in oldAttrs){
       if (oldAttrs.hasOwnProperty(attr)){
         if (!newAttrs.hasOwnProperty(attr)){

spec/javascripts/clear.spec.js

@@ -0,0 +1,54 @@
+describe("clearing all mementos", function(){
+  beforeEach(function(){
+    this.model = new AModel();
+  });
+
+  describe("when clearing", function(){
+    it("should restore to first memento given successive save points", function(){
+      var changed = false;
+      this.model.set({foo: "bar"});
+      this.model.store();
+      this.model.set({foo: "baz"});
+      this.model.store();
+      this.model.set({foo: "qux"});
+      this.model.store();
+
+      this.model.bind("change:foo", function(){
+        changed = true;
+      });
+
+      expect(this.model.get('foo')).toBe('qux');
+      this.model.clear();
+      expect(changed).toBeTruthy();
+      expect(this.model.get('foo')).toBe('bar');
+    });
+
+    it("should lose all other save points", function(){
+      var changed = false;
+      this.model.set({foo: "bar"});
+      this.model.store();
+      this.model.set({foo: "baz"});
+      this.model.store();
+      this.model.set({foo: "qux"});
+      this.model.store();
+
+      this.model.clear();
+      this.model.restore();
+
+      expect(this.model.get('foo')).toBe('bar'); //should not be qux
+    });
+
+    it("should do nothing given no store point", function(){
+      var changed = false;
+      this.model.set({foo: "bar"});
+
+      this.model.bind("change:foo", function(){
+        changed = true;
+      });
+      this.model.clear();
+
+      expect(this.model.get('foo')).toBe('bar');
+      expect(changed).toBeFalsy();
+    });
+  });
+});

spec/javascripts/memento.spec.js

@@ -27,6 +27,19 @@ describe("memento", function(){
     });
   });
 
+  describe("when mementoing once and restoring twice", function(){
+    beforeEach(function(){
+      this.model.set({foo: "bar"});
+      this.model.store();
+    });
+
+    it("should not restore anything", function(){
+      this.model.restore();
+      this.model.restore();
+      expect(this.model.get("foo")).toBe("bar");
+    });
+  });
+
   describe("when mementoing twice and rolling back once", function(){
     beforeEach(function(){
       this.model.set({foo: "bar"});
@@ -84,8 +97,7 @@ describe("memento", function(){
       expect(this.model.get('foo')).toBe('bar');
     });
 
-
-     it("should lose all other save points", function(){
+    it("should lose all other save points", function(){
       var changed = false;
       this.model.set({foo: "bar"});
       this.model.store();
@@ -100,8 +112,6 @@ describe("memento", function(){
       expect(this.model.get('foo')).toBe('bar'); //should not be qux
     });
 
-
-
     it("should do nothing given no store point", function(){
       var changed = false;
       this.model.set({foo: "bar"});