Q: useAttrs() vs $attrs — how do you handle fallthrough attributes in composition API?

**Target Audience:** Vue developers moving to ` ` and the Composition API. Assumes you know what [fallthrough attributes ($attrs)](/interview-question/what-are-fallthrough-attributes-attrs) are; that sibling question covers the inheritance rules themselves. **Difficulty:** Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. Every output in the "Verifi

Q: How would you structure state management for a large Vue app?

**Target Audience:** Mid-level and senior Vue developers preparing for a design-style interview — assumes you know [Pinia](/interview-question/what-is-pinia-and-why-use-it) and [composables](/interview-question/what-are-composables-in-vue). **Difficulty:** Hard > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. The verified outputs come from Vue 3.5.44 and pinia 4.1.0:

Question 1

What changed from Vue 2 to Vue 3, and what does Vue 2 end of life mean?

Accepted Answer

**Target Audience:** Developers who meet Vue 2 code at work, or see Vue 2 tutorials online, and need to explain what is different in Vue 3. Basic Vue knowledge helps but every term is defined. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The comparisons in sections 4 and 5 were not taken from the migration guide: the same code was run on **vue 2.7.16** and **vue 3.5.44** side by side in Node with jsdom, and the outputs are

Question 2

How do you bind classes and styles dynamically?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview. Assumes basic HTML and CSS and a first look at Vue templates.
**Difficulty:** Easy

> **How to read this doc:** Plain language first, then `📌 Interview term:` callouts that give you the exact vocabulary. Every rendered class string, style attribute, warning and compiler line quoted below came from running the code on Vue 3.5.44 (compiled with `@vue/compiler-sfc`, mounted in jsdom).

## 1. Why This Even Matters — A Story First

Imagine a

Question 3

What are scoped styles in Vue?

Accepted Answer

**Target Audience:** Vue developers who write `<style scoped>` and want to know precisely what it does and where its edges are.
**Difficulty:** Easy

> **How to read this doc:** Plain language first, then `📌 Interview term:` callouts. The compiled CSS is real output from `@vue/compiler-sfc` 3.5.44 `compileStyle()` and from a `vite build` (vite 8.3.4, `@vitejs/plugin-vue` 6.0.10). The DOM attributes come from mounting the components in jsdom, and the computed colours were read from the built app

Question 4

How do Transition and TransitionGroup work?

Accepted Answer

**Target Audience:** Developers comfortable with Vue templates and basic CSS transitions who want to know exactly what Vue does during an animation. **Difficulty:** Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. The class sequences in section 4 were recorded on Vue 3.5.44 in jsdom with the repo's verify-vue-example.mjs harness. jsdom runs no CSS

Question 5

How do you set up Vue Router (routes, RouterLink, RouterView, history modes)?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview — assumes basic Vue components, no routing experience required. **Difficulty:** Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. Every output block in this doc was produced by running the code on Vue 3.5.44 and vue-router 5.4.0: a real Vite 8 production build loaded into jsdom, Node scripts on the router

Question 6

What are fallthrough attributes ($attrs)?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview. Assumes you know props and events. **Difficulty:** Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. All rendered HTML and warning text in the "Verified" sections was produced on Vue 3.5.44, with the repo verifier (compiled and mounted in jsdom) and with Vitest and Vue Test Utils. This doc covers the rul

Question 7

useAttrs() vs $attrs — how do you handle fallthrough attributes in composition API?

Accepted Answer

**Target Audience:** Vue developers moving to `

Question 8

When should you use readonly, markRaw, and toRaw in Vue reactivity?

Accepted Answer

**Target Audience:** Vue developers designing composables and stores, or integrating non-Vue libraries. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Warnings, outputs and timings below come from running code on Vue 3.5.44 (Node 22, and jsdom for the component); timings are from one sandbox machine. This page is the **decision guide**. The mechanics are covered by two sibling questions: [What does readonly do in Vue's rea

Question 9

What do markRaw and toRaw do?

Accepted Answer

**Target Audience:** Vue developers integrating third-party objects or debugging identity bugs in reactive state. **Difficulty:** Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every value and error message below was printed by running the code on Vue 3.5.44 in Node 22, or by mounting the SFC in jsdom with the repo verifier. This page explains **how** markRaw and toRaw work. For **when** to choose them, alongside <

Question 10

How would you structure state management for a large Vue app?

Accepted Answer

**Target Audience:** Mid-level and senior Vue developers preparing for a design-style interview — assumes you know [Pinia](/interview-question/what-is-pinia-and-why-use-it) and [composables](/interview-question/what-are-composables-in-vue). **Difficulty:** Hard > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. The verified outputs come from Vue 3.5.44 and pinia 4.1.0:

VUE.JSDECODED.

Easy

What changed from Vue 2 to Vue 3, and what does Vue 2 end of life mean?

How do you bind classes and styles dynamically?

What are scoped styles in Vue?

Medium

How do Transition and TransitionGroup work?

How do you set up Vue Router (routes, RouterLink, RouterView, history modes)?

What are fallthrough attributes ($attrs)?

useAttrs() vs $attrs — how do you handle fallthrough attributes in composition API?

When should you use readonly, markRaw, and toRaw in Vue reactivity?

Hard

What do markRaw and toRaw do?

How would you structure state management for a large Vue app?

How does the Vue compiler optimize templates (static hoisting, patch flags, block tree)?

What are common reactivity caveats in Vue?

How do you diagnose and fix hydration mismatches in Vue SSR / Nuxt 3?