Using stores in components in Vue - Mini Project: Build & Apply

Using stores in components

📖 Scenario: You are building a simple Vue 3 app that tracks a user's favorite color using a store. The store holds the color value and lets components read and update it.

🎯 Goal: Create a Vue 3 component that uses a store to display and update the favorite color. The component will show the current color and have a button to change it.

📋 What You'll Learn

Create a Pinia store with a state variable favoriteColor set to 'blue'

Add a function in the store called changeColor that sets favoriteColor to 'red'

Create a Vue component that imports and uses the store

Display the current favoriteColor in the component

Add a button in the component that calls changeColor when clicked

💡 Why This Matters

🌍 Real World

Stores help manage shared data in Vue apps, like user preferences or app settings, so components stay in sync easily.

💼 Career

Understanding how to use Pinia stores is important for Vue developers to build scalable and maintainable applications.

1

Create the Pinia store with initial state

Create a Pinia store named useColorStore using defineStore. Inside, define a state with a variable favoriteColor set to the string 'blue'.

Vue

// Your code here to create the Pinia store with favoriteColor state

Hint

Use defineStore from Pinia and return an object with favoriteColor set to 'blue' inside state.

2

Add a function to change the color in the store

Inside the useColorStore Pinia store, add an actions section. Define a function called changeColor that sets this.favoriteColor to 'red'.

Vue

import { defineStore } from 'pinia'

export const useColorStore = defineStore('color', {
  state: () => ({
    favoriteColor: 'blue'
  }),
  // Add actions here
  actions: {
    // Your code here
  }
})

Hint

Inside actions, write a function changeColor that updates this.favoriteColor to 'red'.

3

Import and use the store in a Vue component

Create a Vue 3 component using <script setup>. Import useColorStore from the store file. Call useColorStore() and assign it to a constant named colorStore.

Vue

// Your code here to import and use the store

Hint

Use import { useColorStore } from './store' and then call useColorStore() inside <script setup>.

4

Display the color and add a button to change it

In the Vue component template, display the current color using {{ colorStore.favoriteColor }}. Add a button with the text Change Color that calls colorStore.changeColor when clicked.

Vue

Hint

Use mustache syntax to show colorStore.favoriteColor and add a button with @click="colorStore.changeColor".

Practice

1. What is the main purpose of using a store in a Vue component?

easy

A. To share and manage state across multiple components easily

B. To style components with CSS variables

C. To handle component lifecycle hooks

D. To define routes for navigation

Solution

1. Step 1: Understand what a store does

   A store holds shared data that multiple components can access and update.

2. Step 2: Identify the purpose in Vue components

   Stores help components share and manage state without passing props or events repeatedly.

3. Final Answer:

   To share and manage state across multiple components easily -> Option A

4. Quick Check:

   Store = Shared state management [OK]

Hint: Stores share data between components without props [OK]

Common Mistakes:

• Confusing stores with styling or routing
• Thinking stores handle lifecycle hooks
• Assuming stores are only for single components

2. Which is the correct way to import and use a Pinia store inside a Vue component's setup() function?

easy

A. import store from 'pinia'

B. const store = createStore()

C. const store = useStore()

D. const store = new Store()

Solution

1. Step 1: Recall Pinia store usage

   Pinia stores are accessed inside components by calling the store function, usually named useStore().

2. Step 2: Check the options

   Only const store = useStore() correctly calls the store function inside setup().

3. Final Answer:

   const store = useStore() -> Option C

4. Quick Check:

   Use useStore() to access store [OK]

Hint: Call useStore() inside setup() to get the store [OK]

Common Mistakes:

• Trying to import store directly from 'pinia'
• Using createStore() which is Vuex syntax
• Using new Store() which is not valid in Pinia

3. Given this Pinia store code:

import { defineStore } from 'pinia'
export const useCounterStore = defineStore('counter', {
  state: () => ({ count: 0 }),
  actions: {
    increment() { this.count++ }
  }
})

And this component code:

const counter = useCounterStore()
counter.increment()
console.log(counter.count)

What will be logged to the console?

medium

A. NaN

B. 0

C. undefined

D. 1

Solution

1. Step 1: Understand the store state and action

   The store starts with count = 0. Calling increment() increases count by 1.

2. Step 2: Trace the component code

   After calling counter.increment(), counter.count becomes 1, so logging it prints 1.

3. Final Answer:

   1 -> Option D

4. Quick Check:

   Increment changes count from 0 to 1 [OK]

Hint: increment() adds 1 to count, so output is 1 [OK]

Common Mistakes:

• Expecting count to stay 0 without calling increment
• Confusing state with undefined
• Thinking increment returns a value

4. What is wrong with this Vue component code using a Pinia store?

import { useCounterStore } from '@/stores/counter'
export default {
  setup() {
    const counter = useCounterStore
    counter.increment()
    return { counter }
  }
}

medium

A. useCounterStore is not called as a function

B. increment() is not a valid action

C. counter should be imported from 'pinia' instead

D. setup() should return a function

Solution

1. Step 1: Check how the store is used

   The code assigns counter = useCounterStore without parentheses, so it stores the function itself, not the store instance.

2. Step 2: Understand the effect

   Calling counter.increment() fails because counter is a function, not the store object.

3. Final Answer:

   useCounterStore is not called as a function -> Option A

4. Quick Check:

   Call useCounterStore() to get store instance [OK]

Hint: Always call useCounterStore() with () [OK]

Common Mistakes:

• Forgetting parentheses when calling store function
• Assuming increment() is invalid
• Confusing import source for store

5. You want to create a Vue component that uses a Pinia store to track a list of tasks. You need to add a new task only if it is not empty and not already in the list. Which code snippet correctly uses the store inside setup() to achieve this?

hard

A. const taskStore = useTaskStore
function addTask(task) {
if (taskStore.tasks.indexOf(task) === -1) {
taskStore.tasks.push(task)
}
}

B. const taskStore = useTaskStore()
function addTask(task) {
if (task && !taskStore.tasks.includes(task)) {
taskStore.tasks.push(task)
}
}

C. const taskStore = useTaskStore()
function addTask(task) {
if (task !== '') {
taskStore.tasks = [...taskStore.tasks, task]
}
}

D. const taskStore = useTaskStore()
function addTask(task) {
taskStore.tasks.push(task)
}

Solution

1. Step 1: Check store usage and function call

   const taskStore = useTaskStore()
   function addTask(task) {
     if (task && !taskStore.tasks.includes(task)) {
       taskStore.tasks.push(task)
     }
   

   correctly calls useTaskStore() to get the store instance and defines addTask with proper checks.

2. Step 2: Verify conditions for adding task

   It checks if task is not empty and not already in taskStore.tasks before pushing, preventing duplicates and empty entries.

3. Final Answer:

   correctly uses the store and conditions to add tasks safely -> Option B

4. Quick Check:

   Call store with () and check conditions before push [OK]

Hint: Call store with () and check duplicates before push [OK]

Common Mistakes:

• Not calling useTaskStore() as a function
• Not checking for empty or duplicate tasks
• Replacing tasks array instead of pushing