Vue.js High-Level Interview Q&A (Top 30)

1. What is Vue.js architecture based on?

Vue follows the MVVM (Model-View-ViewModel) pattern, where:

Model → Data
View → UI (template)
ViewModel → Vue instance (reactivity bridge)

2. Explain Vue reactivity system (deep concept)

Vue uses:

Vue 2: Object.defineProperty
Vue 3: Proxy

Vue tracks dependencies and automatically updates DOM when data changes.

3. What is Virtual DOM in Vue?

Virtual DOM is a lightweight JS representation of real DOM.

👉 Vue compares old vs new VDOM (diffing) and updates only changed parts.

4. Difference between Vue 2 and Vue 3?

Feature	Vue 2	Vue 3
Reactivity	defineProperty	Proxy
API	Options API	Composition API
Performance	Moderate	Faster
Tree-shaking	No	Yes

5. What is Composition API?

A new way to organize logic using:

setup() {
  const count = ref(0)
  return { count }
}

Better for:

Code reuse
Large projects

6. Difference: ref vs reactive?

ref() → primitive values
reactive() → objects

7. What is computed vs watch?

computed: cached, derived state
watch: side effects

8. What is nextTick?

Executes code after DOM update:

await nextTick()

9. Explain lifecycle hooks (Vue 3)

onMounted
onUpdated
onUnmounted

10. What is v-model internally?

Two-way binding using:

:modelValue + @update:modelValue

11. What is Teleport?

Render component outside DOM hierarchy:

<teleport to="body">

12. What are slots?

Used for content distribution:

default
named
scoped

13. What is scoped slot?

Pass data from child → parent via slot.

14. What is provide/inject?

Dependency injection system in Vue.

15. What is Pinia?

Modern state management (Vuex replacement)

16. Difference: Vuex vs Pinia?

Pinia → simpler, modular, no mutations
Vuex → complex, strict pattern

17. What is SSR?

Server Side Rendering improves:

SEO
performance

Used via Nuxt.js

18. What is hydration?

Client attaches JS to SSR HTML.

19. What is Suspense?

Handles async components:

<Suspense>

20. What is KeepAlive?

Caches component state.

21. What is dynamic component?

<component :is="compName" />

22. What are directives?

Custom behavior:

v-focus

23. What is mixin problem?

Naming conflicts
Hard to debug

👉 replaced by Composition API

24. What is tree-shaking?

Removes unused code → smaller bundle.

25. What is code splitting?

Lazy loading components:

const Comp = () => import('./Comp.vue')

26. What is emits in Vue 3?

Declare events:

emits: ['submit']

27. What is shallowRef?

Tracks only top-level changes.

28. What is markRaw?

Exclude object from reactivity.

29. What is effect scope?

Control lifecycle of reactive effects.

30. Performance optimization techniques?

Lazy loading
v-memo
keep-alive
debounce watch
optimize computed

💡 Pro Interview Tips

Always compare Vue 2 vs Vue 3
Explain why, not just what
Mention real-world use cases
Talk about performance & scalability

30 high-level Vue.js interview questions & answers