Introduce a tidy-up method to remove old features

.editorconfig

@@ -0,0 +1,3 @@
+[*.ts]
+indent_size = 4
+indent_style = space

spec/FeatureToggleService.spec.ts

@@ -3,6 +3,7 @@ import { FeatureToggleService } from '../src/FeatureToggleService';
 describe('Feature toggling', () => {
     beforeEach(() => {
         localStorage.clear();
+        FeatureToggleService.clearInternalFeatureList();
     });
 
     it('can register a feature', () => {
@@ -32,7 +33,7 @@ describe('Feature toggling', () => {
         expect(JSON.parse(localStorage.getItem('_feature.foo')).enabled).toBe(true);
     });
 
-    it('it considers a feature disabled if it is not set to on', () => {
+    it('considers a feature disabled if it is not set to on', () => {
         const service = new FeatureToggleService();
 
         service.register({
@@ -43,7 +44,7 @@ describe('Feature toggling', () => {
         expect(service.check('foo')).toBe(false);
     });
 
-    it('it considers a feature disabled if the localStorage key is missing', () => {
+    it('considers a feature disabled if the localStorage key is missing', () => {
         const service = new FeatureToggleService();
 
         service.register({
@@ -56,7 +57,7 @@ describe('Feature toggling', () => {
         expect(service.check('foo')).toBe(false);
     });
 
-    it('it considers a feature enabled if it is set to on', () => {
+    it('considers a feature enabled if it is set to on', () => {
         const service = new FeatureToggleService();
 
         service.register({
@@ -71,4 +72,23 @@ describe('Feature toggling', () => {
 
         expect(service.check('foo')).toBe(true);
     });
+
+    describe('tidyUp method', () => {
+        it('removes the features that is not registered from localStorage', () => {
+            localStorage.setItem('_feature.some_old_feature', JSON.stringify({
+                name: 'Old feature that we will no longer register',
+                enabled: true,
+            }));
+
+            const service = new FeatureToggleService();
+            service.register({
+                name: 'Some new feature',
+                key: 'some_new_feature',
+            });
+
+            service.tidyUpLocalStorageData();
+
+            expect(localStorage.getItem('_feature.some_old_feature')).toBeNull();
+        });
+    });
 });

src/FeatureToggleService.ts

@@ -12,6 +12,16 @@ export class FeatureToggleService {
         localStorage.setItem('_feature._enabled', JSON.stringify(true));
     }
 
+    /**
+     * Clears the internal feature list. This only exists to be used in tests.
+     * Do not use in production code. No really, don't.
+     *
+     * @private
+     */
+    static clearInternalFeatureList() {
+        features.clear();
+    }
+
     register(feature: Feature) {
         if (!feature.name) {
             feature.name = feature.key;
@@ -27,6 +37,29 @@ export class FeatureToggleService {
         }
     }
 
+    /**
+     * This method is used to tidy up localStorage. It will remove any features
+     * that are no longer registered.
+     *
+     * You should only call this method after registering all features.
+     */
+    tidyUpLocalStorageData() {
+        const registeredFeatures = Array.from(features.keys());
+        const keysInLocalStorage = Object.keys(localStorage)
+            .filter(key =>
+                key.startsWith(this.localStoragePrefix) &&
+                key !== `${this.localStoragePrefix}._enabled`
+            );
+
+        keysInLocalStorage.forEach(key => {
+           const feature = key.replace(`${this.localStoragePrefix}.`, '');
+
+           if (registeredFeatures.indexOf(feature) === -1) {
+               localStorage.removeItem(key);
+           }
+        });
+    }
+
     check(featureKey: string): boolean {
         if (!features.has(featureKey)) {
             console.warn(`The feature ${featureKey} has not been registered`);
@@ -41,4 +74,4 @@ export class FeatureToggleService {
     private localStorageKey(featureKey: string): string {
         return `${this.localStoragePrefix}.${featureKey}`;
     }
-}
+}