Small refactor to improve readability

app/app.js

 import React, { Component } from 'react';
-import { BackAndroid, AsyncStorage } from 'react-native';
+import { AsyncStorage } from 'react-native';
 import { createStore, applyMiddleware, combineReducers } from 'redux';
 import { Provider } from 'react-redux';
 import thunk from 'redux-thunk';
 
 import * as reducers from './reducers';
 import ReduxNavigator from './components/navigator';
-import { back } from './actions/navigation';
 import { initLogin } from './actions/login';
 
 const createStoreWithMiddleware = applyMiddleware(thunk)(createStore);
@@ -15,27 +14,18 @@ const store = createStoreWithMiddleware(reducer);
 
 const USERNAMEKEY = '@MyStore:username';
 const TOKENKEY = '@MyStore:token';
-
-BackAndroid.addEventListener('hardwareBackPress', () => {
-  if (store.getState().navigation.previousScenes.length === 0) {
-    return false;
-  }
-  store.dispatch(back());
-  return true;
-});
+const pairsToObject = (obj, pair) => {
+  const obj2 = { ...obj };
+  obj2[pair[0]] = pair[1];
+  return obj2;
+};
 
 class Main extends Component {
   componentDidMount() {
     AsyncStorage.multiGet([USERNAMEKEY, TOKENKEY])
       .then(
         (result) => {
-          // Transform [key, value] pairs into object, for easier access
-          const values = result.reduce((obj, pair) => {
-            const obj2 = { ...obj };
-            obj2[pair[0]] = pair[1];
-            return obj2;
-          }, {});
-
+          const values = result.reduce(pairsToObject, {});
           const username = values[USERNAMEKEY];
           const token = values[TOKENKEY];