Using stores in components in Vue - Performance & Optimization

Performance: Using stores in components

MEDIUM IMPACT

Using stores in Vue components affects how state updates trigger component re-renders and how efficiently data flows through the app.

Accessing store state in multiple components causing unnecessary re-renders

Vue

import { useStore } from 'vuex';
import { computed } from 'vue';
export default {
  setup() {
    const store = useStore();
    const count = computed(() => store.getters['getCount']);
    return { count };
  }
}

Using getters or selective computed properties limits re-renders to only when relevant state changes.

📈 Performance Gainreduces unnecessary re-renders, improving input responsiveness

Accessing store state in multiple components causing unnecessary re-renders

Vue

import { useStore } from 'vuex';
import { computed } from 'vue';
export default {
  setup() {
    const store = useStore();
    const count = computed(() => store.state.count);
    return { count };
  }
}

Directly using the entire store state or large objects causes all dependent components to re-render on any state change, even unrelated ones.

📉 Performance Costtriggers re-render for all components using store state on any mutation

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Direct store state access in many components	High (many reactive dependencies)	High (many re-renders)	High (many paints)	[X] Bad
Using selective getters and mutations	Low (minimal reactive dependencies)	Low (targeted re-renders)	Low (fewer paints)	[OK] Good

Rendering Pipeline

When a store state changes, Vue tracks dependencies and schedules component re-renders. Efficient store usage minimizes the number of components that re-render and reduces layout recalculations.

→Dependency Tracking

→Component Re-render

→Layout

→Paint

⚠️ BottleneckComponent Re-render stage is most expensive due to unnecessary updates.

Core Web Vital Affected

INP

Using stores in Vue components affects how state updates trigger component re-renders and how efficiently data flows through the app.

Optimization Tips

1Use computed getters to access only needed store state in components.

2Always update store state via mutations to ensure proper tracking.

3Avoid accessing large or entire store state directly in multiple components.

Performance Quiz - 3 Questions

What is a performance risk when directly accessing large store state objects in many components?

A Components never update

B Store state becomes immutable

C All components re-render on any store change

D Store size increases

DevTools: Performance

How to check: Record a performance profile while interacting with components that use the store. Look for frequent component re-renders and long scripting times.

What to look for: Check the flame chart for repeated renders of components on unrelated store changes indicating inefficient store usage.

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