What are the key differences between Vue 2 and Vue 3?
Compare Vue 2 and Vue 3: Proxy reactivity, the Composition API, Fragments, Teleport, Suspense, TypeScript, and smaller faster bundles for modern apps.
Expected Interview Answer
Vue 3 is a rewrite that introduces the Composition API, a Proxy-based reactivity system, better TypeScript support, and a smaller, faster runtime, while remaining largely compatible with Vue 2's Options API. The biggest practical changes are how you organize component logic and how reactivity works under the hood.
Vue 2 used Object.defineProperty for reactivity, which could not detect property additions or array index changes without special helpers; Vue 3 uses Proxy, tracking those automatically. Vue 3 adds the Composition API (setup, ref, reactive, composables) for better logic reuse than mixins, supports multiple root nodes via Fragments, and ships Teleport and Suspense. It has a tree-shakable core, a faster virtual DOM, first-class TypeScript, and global API changes like createApp instead of new Vue. Vue 2 reached end of life at the end of 2023, so new projects should use Vue 3.
- Automatic reactivity for added properties and array indexes via Proxy
- Better logic reuse and organization with the Composition API
- Smaller, tree-shakable bundles and faster rendering
- First-class TypeScript and improved editor support
- New primitives: Fragments, Teleport, and Suspense
AI Mentor Explanation
Vue 2 to Vue 3 is like upgrading from a rigid batting order to a flexible, situation-based lineup. Vue 2's Options API is a fixed order — openers, middle, tail in set slots. Vue 3's Composition API lets you group players by the match situation, reusing a proven partnership across games. The Proxy reactivity is a smarter scoreboard that notices a new extra or run automatically instead of needing a manual correction.
Step-by-Step Explanation
Step 1
Reactivity engine
Vue 2 uses Object.defineProperty (misses new props and array index changes); Vue 3 uses Proxy, tracking them automatically.
Step 2
Component API
Vue 3 adds the Composition API (setup, ref, reactive, composables) alongside the Options API for better logic reuse than mixins.
Step 3
New built-ins
Vue 3 supports Fragments (multiple root nodes), Teleport for portaling markup, and Suspense for async components.
Step 4
Performance and size
Vue 3 has a tree-shakable core, a faster virtual DOM, and smaller bundles than Vue 2.
Step 5
Global API and tooling
Vue 3 uses createApp instead of new Vue, ships first-class TypeScript, and Vue 2 hit end of life in Dec 2023.
What Interviewer Expects
- Proxy vs Object.defineProperty reactivity difference
- What the Composition API adds over the Options API
- Knowledge of Fragments, Teleport, and Suspense
- Awareness of performance and bundle-size improvements
- Global API and TypeScript changes, plus Vue 2 end of life
Common Mistakes
- Claiming the Options API was removed in Vue 3
- Not knowing why Vue 2 needed Vue.set for new properties
- Confusing the Composition API with a required rewrite of all code
- Forgetting Vue 3 supports multiple root nodes
- Thinking Vue 3 dropped backward compatibility entirely
Best Answer (HR Friendly)
“Vue 3 is a modernized version of Vue 2. It changes how the framework tracks data so it notices more changes automatically, and it adds a new, more flexible way to organize and reuse component logic. It is also smaller and faster, and Vue 2 is no longer maintained, so new apps use Vue 3.”
Code Example
// Vue 2 / Options API
export default {
data() {
return { count: 0 }
},
methods: {
increment() { this.count++ },
},
}
// Vue 3 / Composition API
import { ref } from 'vue'
export default {
setup() {
const count = ref(0)
const increment = () => count.value++
return { count, increment }
},
}Follow-up Questions
- Why could Vue 2 not detect new object properties without Vue.set?
- How does the Composition API improve logic reuse over mixins?
- What problems do Teleport and Suspense solve?
- Why does Vue 3 produce smaller bundles than Vue 2?
- Can you still use the Options API in Vue 3?
MCQ Practice
1. What reactivity mechanism does Vue 3 use instead of Object.defineProperty?
Vue 3 uses JavaScript Proxy, which can intercept property additions, deletions, and array index changes that Object.defineProperty could not track.
2. Which feature is new in Vue 3?
Teleport (rendering markup elsewhere in the DOM) is new in Vue 3, along with Fragments and Suspense; the Options API and mixins existed in Vue 2.
3. In Vue 2, why did adding a new property to a reactive object not update the view?
Vue 2's Object.defineProperty-based reactivity only tracked properties present at init, so new ones needed Vue.set; Vue 3's Proxy handles them automatically.
Flash Cards
Reactivity: Vue 2 vs Vue 3 — Vue 2 uses Object.defineProperty (misses new props/array indexes); Vue 3 uses Proxy, tracking them automatically.
Composition API — New in Vue 3: setup, ref, reactive, and composables for better logic reuse than mixins. Options API still works.
New Vue 3 built-ins — Fragments (multiple root nodes), Teleport (portal markup), and Suspense (async component fallback).
App bootstrap change — Vue 3 uses createApp(App).mount('#app') instead of Vue 2's new Vue({...}).
Vue 2 status — Vue 2 reached end of life on Dec 31, 2023; new projects should use Vue 3.
Continue Learning
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