Persisting store state in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'persisting store state' mean in Vue applications?

It means saving the data in the store so it stays even after the page reloads or the user closes the browser. This helps keep the app's state consistent.

beginner

Which browser storage options are commonly used to persist Vue store state?

LocalStorage and SessionStorage are common. LocalStorage keeps data even after closing the browser, while SessionStorage clears data when the tab closes.

intermediate

How can you automatically save Vue store state changes to LocalStorage?

You can watch the store state and save it to LocalStorage whenever it changes, or use plugins like vuex-persistedstate that handle this for you.

intermediate

What is a simple way to restore persisted state when a Vue app starts?

When the app loads, read the saved state from LocalStorage and replace the store's state with it, so the app continues where it left off.

advanced

Why should you be careful about what data you persist in the store?

Because sensitive data saved in LocalStorage can be accessed by anyone using the browser. Also, large data can slow down loading and cause bugs if outdated.

Which Vue plugin helps automatically persist store state to LocalStorage?

A vue-router

B vuex-persistedstate

C vue-loader

D vuex-logger

vuex-persistedstate is designed to save and restore Vuex store state automatically using browser storage.

What happens to data in SessionStorage when the browser tab closes?

A It is encrypted

B It is saved permanently

C It is sent to the server

D It is cleared

SessionStorage data is cleared when the browser tab or window closes.

Why might you not want to persist all Vue store data?

A Because it can cause security risks and slow loading

B Because Vue does not support persistence

C Because LocalStorage is too small

D Because persistence is automatic

Persisting sensitive or large data can cause security issues and performance problems.

Which method is commonly used to restore persisted state in Vuex?

A Replacing the store state on app start

B Using Vue Router guards

C Calling a Vue lifecycle hook

D Using CSS variables

Restoring persisted state usually involves replacing the Vuex store state with saved data when the app loads.

What is the main difference between LocalStorage and SessionStorage?

A SessionStorage is shared across tabs; LocalStorage is not

B SessionStorage is faster than LocalStorage

C LocalStorage persists after browser closes; SessionStorage does not

D LocalStorage encrypts data; SessionStorage does not

LocalStorage keeps data even after closing the browser, while SessionStorage clears data when the tab closes.

Explain how you would implement persisting Vue store state using LocalStorage.

Think about saving data when it changes and loading it back when the app starts.

What are the risks and best practices when persisting store state in a Vue app?

Consider security and performance when saving data.

Practice

1. What is the main purpose of persisting store state in a Vue application?

easy

A. To speed up the app by caching components

B. To keep the app data saved even after refreshing or closing the browser

C. To automatically update the UI without user input

D. To prevent users from logging out

Solution

1. Step 1: Understand what persisting store state means

   Persisting store state means saving the app's data so it does not disappear when the page reloads or the browser closes.

2. Step 2: Identify the main benefit

   This helps keep user data or app settings intact, improving user experience.

3. Final Answer:

   To keep the app data saved even after refreshing or closing the browser -> Option B

4. Quick Check:

   Persisting state = saving data after refresh [OK]

Hint: Persisting means saving data beyond page reloads [OK]

Common Mistakes:

• Confusing persisting with caching UI components
• Thinking it automatically updates UI without user action
• Believing it prevents user logout directly

2. Which of the following is the correct way to add the vuex-persistedstate plugin to a Vuex store?

easy

A. import createPersistedState from 'vuex-persistedstate';

const store = createStore({
plugins: createPersistedState
});

B. import createPersistedState from 'vuex-persistedstate';

const store = createStore({
persist: createPersistedState()
});

C. import createPersistedState from 'vuex-persistedstate';

const store = createStore({
plugins: [createPersistedState()]
});

D. import createPersistedState from 'vuex-persistedstate';

const store = createStore({
plugins: [createPersistedState]
});

Solution

1. Step 1: Recall the plugin usage syntax

   The vuex-persistedstate plugin is imported as a function and added inside the plugins array when creating the store.

2. Step 2: Check the correct syntax

   import createPersistedState from 'vuex-persistedstate'; const store = createStore({ plugins: [createPersistedState()] }); correctly imports and calls createPersistedState() inside the plugins array.

3. Final Answer:

   import createPersistedState from 'vuex-persistedstate'; const store = createStore({ plugins: [createPersistedState()] }); -> Option C

4. Quick Check:

   Plugin added as function in plugins array [OK]

Hint: Plugins go inside plugins array, called as functions [OK]

Common Mistakes:

• Putting plugin directly as object property instead of in plugins array
• Not calling the plugin function with ()
• Passing plugin without wrapping in array

3. Given this Vuex store setup with vuex-persistedstate:

import { createStore } from 'vuex';
import createPersistedState from 'vuex-persistedstate';

const store = createStore({
  state() {
    return { count: 0 };
  },
  mutations: {
    increment(state) {
      state.count++;
    }
  },
  plugins: [createPersistedState()]
});

store.commit('increment');

// After page reload, what is the value of store.state.count?

medium

A. 1

B. Error

C. undefined

D. 0

Solution

1. Step 1: Understand what happens on commit

   The mutation increment increases count from 0 to 1.

2. Step 2: Effect of vuex-persistedstate plugin

   This plugin saves the state to localStorage, so after page reload, the state is restored with count still 1.

3. Final Answer:

   1 -> Option A

4. Quick Check:

   Persisted state restores count = 1 after reload [OK]

Hint: Persisted state keeps mutations after reload [OK]

Common Mistakes:

• Assuming state resets to initial value after reload
• Thinking plugin does not save mutations
• Confusing undefined or error with normal behavior

4. You added vuex-persistedstate to your Vuex store but the state is not saved after refresh. Which of these is the most likely cause?

medium

A. You forgot to call the plugin function inside the plugins array

B. You did not import Vuex correctly

C. You used mutations instead of actions

D. You did not define the initial state

Solution

1. Step 1: Check plugin usage

   If the plugin is added without calling it as a function (missing parentheses), it won't activate and save state.

2. Step 2: Verify other options

   Importing Vuex correctly, using mutations, and defining initial state are unrelated to plugin activation.

3. Final Answer:

   You forgot to call the plugin function inside the plugins array -> Option A

4. Quick Check:

   Plugin must be called as function to work [OK]

Hint: Always call plugin with () inside plugins array [OK]

Common Mistakes:

• Adding plugin without parentheses
• Blaming mutations or initial state for persistence issues
• Ignoring plugin import errors

5. You want to persist only the user part of your Vuex state and store it in sessionStorage instead of localStorage. Which is the correct way to configure vuex-persistedstate?

hard

A. plugins: [createPersistedState({ only: ['user'], storage: window.sessionStorage })]

B. plugins: [createPersistedState({ paths: ['user'], storage: 'sessionStorage' })]

C. plugins: [createPersistedState({ keys: ['user'], storage: sessionStorage })]

D. plugins: [createPersistedState({ paths: ['user'], storage: window.sessionStorage })]

Solution

1. Step 1: Use the correct option to select parts of state

   The paths option specifies which parts of the state to save, so paths: ['user'] is correct.

2. Step 2: Set storage to sessionStorage correctly

   The storage option expects the storage object, so window.sessionStorage is correct.

3. Final Answer:

   plugins: [createPersistedState({ paths: ['user'], storage: window.sessionStorage })] -> Option D

4. Quick Check:

   Use paths and window.sessionStorage for selective session storage [OK]

Hint: Use paths array and window.sessionStorage for selective session saving [OK]

Common Mistakes:

• Using string 'sessionStorage' instead of window.sessionStorage object
• Using wrong option names like only or keys
• Not specifying paths to limit saved state