Fix last tab is undefined

src/background/infrastructures/memory-storage.js

@@ -10,6 +10,10 @@ export default class MemoryStorage {
   }
 
   get(name) {
-    return JSON.parse(db[name]);
+    let data = db[name];
+    if (!data) {
+      return undefined;
+    }
+    return JSON.parse(data);
   }
 }

src/background/usecases/operation.js

@@ -183,7 +183,9 @@ export default class OperationInteractor {
 
   onTabSelected(tabId) {
     let lastId = this.cache.get(CURRENT_SELECTED_KEY);
+    if (lastId) {
       this.cache.set(LAST_SELECTED_KEY, lastId);
+    }
     this.cache.set(CURRENT_SELECTED_KEY, tabId);
   }
 }

test/background/infrastructures/memory-storage.test.js

@@ -15,6 +15,11 @@ describe("background/infrastructures/memory-storage", () => {
     expect(cache.get('object')).to.deep.equal({ hello: '123' });
   });
 
+  it('returns undefined if no keys', () => {
+    let cache = new MemoryStorage();
+    expect(cache.get('no-keys')).to.be.undefined;
+  })
+
   it('stored on shared memory', () => {
     let cache = new MemoryStorage();
     cache.set('red', 'apple');