Using stores in components in Vue - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What will this Vue component display?

Given the following Vue 3 component using Pinia store, what will be rendered inside the <div>?

Vue

import { defineComponent } from 'vue';
import { useCounterStore } from '@/stores/counter';

export default defineComponent({
  setup() {
    const counter = useCounterStore();
    return { counter };
  },
  template: `<div>{{ counter.count }}</div>`
});

// Pinia store definition:
// import { defineStore } from 'pinia';
// export const useCounterStore = defineStore('counter', {
//   state: () => ({ count: 5 }),
//   actions: {
//     increment() { this.count++; }
//   }
// });

A 5

B 0

C undefined

D Error: counter is not defined

💡 Hint

Look at the initial state of the store's count property.

The Pinia store useCounterStore initializes count to 5. The component accesses counter.count and displays it, so the output is 5.

❓ state_output

intermediate

What is the value of message after clicking the button?

Consider this Vue 3 component using a Pinia store. What will be the value of message after the button is clicked once?

Vue

import { defineComponent, ref } from 'vue';
import { useMessageStore } from '@/stores/message';

export default defineComponent({
  setup() {
    const store = useMessageStore();
    const message = ref(store.text);
    function update() {
      store.updateText('Hello Vue!');
      message.value = store.text;
    }
    return { message, update };
  },
  template: `<div><p>{{ message }}</p><button @click="update">Update</button></div>`
});

// Pinia store definition:
// import { defineStore } from 'pinia';
// export const useMessageStore = defineStore('message', {
//   state: () => ({ text: 'Initial' }),
//   actions: {
//     updateText(newText) { this.text = newText; }
//   }
// });

A Error: message is not reactive

B Hello Vue!

C undefined

D Initial

💡 Hint

Think about how message is assigned and updated.

The message ref is initialized with the store's text value but does not reactively track store changes. Updating the store's text does not update message automatically. So after clicking, message remains 'Initial'.

📝 Syntax

advanced

Which option correctly imports and uses a Pinia store in a Vue 3 component?

Identify the correct way to import and use a Pinia store named useTodoStore inside a Vue 3 component's setup function.

A

import { useTodoStore } from '@/stores/todo';

export default {
  setup() {
    const todoStore = useTodoStore;
    return { todoStore };
  }
};

B

import useTodoStore from '@/stores/todo';

export default {
  setup() {
    const todoStore = useTodoStore();
    return { todoStore };
  }
};

C

import { useTodoStore } from '@/stores/todo';

export default {
  setup() {
    const todoStore = useTodoStore();
    return { todoStore };
  }
};

D

import { useTodoStore } from '@/stores/todo';

export default {
  setup() {
    const todoStore = useTodoStore();
  }
};

💡 Hint

Remember how to import named exports and call functions inside setup.

Option C correctly imports the named export useTodoStore and calls it inside setup. Option C imports as default which is incorrect. Option C assigns the function itself without calling it. Option C does not return the store, so it won't be accessible in the template.

🔧 Debug

advanced

Why does this Vue component fail to update the store state reactively?

Examine the code below. The component tries to update the Pinia store's count when the button is clicked, but the displayed count does not change. What is the cause?

Vue

import { defineComponent } from 'vue';
import { useCounterStore } from '@/stores/counter';

export default defineComponent({
  setup() {
    const counter = useCounterStore();
    function increment() {
      counter.count += 1;
    }
    return { counter, increment };
  },
  template: `<div><p>{{ counter.count }}</p><button @click="increment">Add</button></div>`
});

// Pinia store:
// export const useCounterStore = defineStore('counter', {
//   state: () => ({ count: 0 }),
//   actions: {
//     increment() { this.count++; }
//   }
// });

A Directly modifying <code>counter.count</code> bypasses Pinia's reactivity; must use store action.

B The store is not properly imported, causing reactivity to fail.

C The template syntax is incorrect; must use <code>v-text</code> instead of interpolation.

D The <code>increment</code> function is not returned from <code>setup</code>.

💡 Hint

Consider how Pinia tracks changes and the recommended way to update state.

Pinia recommends updating state via actions to ensure reactivity and proper tracking. Directly modifying counter.count may not trigger updates in some setups. Using the store's increment action ensures reactive updates.

🧠 Conceptual

expert

What is the main benefit of using Pinia stores in Vue components?

Choose the best explanation for why developers use Pinia stores in Vue 3 applications.

A Pinia replaces Vue Router to handle navigation between pages.

B Pinia centralizes state management, making state reactive and shared across components easily.

C Pinia automatically generates UI components based on state definitions.

D Pinia compiles Vue templates into optimized JavaScript functions.

💡 Hint

Think about what state management means in an app.

Pinia is a state management library that centralizes and shares reactive state across Vue components. It does not generate UI, handle routing, or compile templates.