Previous selected tab as redux

src/background/reducers/tab.js

@@ -0,0 +1,19 @@
+import actions from 'background/actions';
+
+const defaultState = {
+  previousSelected: -1,
+  currentSelected: -1,
+};
+
+export default function reducer(state = defaultState, action = {}) {
+  switch (action.type) {
+  case actions.TAB_SELECTED:
+    return {
+      previousSelected: state.currentSelected,
+      currentSelected: action.tabId,
+    };
+  default:
+    return state;
+  }
+}
+