Question 1

How do defineProps and defineEmits work in <script setup>?

Accepted Answer

**Target Audience:** Vue 3 developers using `<script setup>` who want to understand the two macros they write in almost every component.
**Difficulty:** Easy

> **How to read this doc:** Plain language first, then `📌 Interview term:` callouts. All compiled output and compiler errors come from `@vue/compiler-sfc` 3.5.44 `compileScript()`; runtime logs from a two-component app compiled the same way and mounted in jsdom; type errors from `vue-tsc` 3.3.13.

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

Question 2

How does Vue's reactivity system work?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview — assumes basic JavaScript objects and functions, no Vue internals required. **Difficulty:** Medium > **How to read this doc:** Each idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. Every output block below was produced by running the code on Vue 3.5.44: plain reactivity with node, components compiled with @vue/compiler-s

Question 3

What is the difference between watch and watchEffect?

Accepted Answer

**Target Audience:** Vue developers who reach for watchers and want to choose between the two on purpose rather than by habit. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary interviewers listen for. Every output below was produced on Vue 3.5.44, with node for the reactivity probe and with @vue/compiler-sfc plus jsdom for the components. This page is about the *tracking model*; t

Question 4

How do dynamic routes and route params work in Vue Router?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview who has a basic router set up — see [how to set up Vue Router](/interview-question/how-do-you-set-up-vue-router-routes-routerlink-routerview-history-modes) if not. **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 was produced by running the code on Vue 3.5.44 and vue-ro

Question 5

What are provide and inject?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview. Assumes you know props and `ref()`. **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 "Verified" sections was produced on Vue 3.5.44: the runnable example with the repo verifier (compiled and mounted in jsdom), the app-level behaviour with a Node script against the sam

Question 6

How do you handle errors in Vue (onErrorCaptured, app.config.errorHandler)?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview who knows [the component lifecycle](/interview-question/what-are-vue-lifecycle-hooks) — no error-monitoring 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 was produced on Vue 3.5.44: the propagation scripts ran in Node with jsdom, once in development an

Question 7

What is the difference between computed and watch?

Accepted Answer

**Target Audience:** Vue developers who use both APIs and want a crisp rule for choosing, plus the reasons behind it. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the precise vocabulary. Every output below was produced on Vue 3.5.44: the probes with node, the component by compiling it with @vue/compiler-sfc and typing into it in jsdom. ## 1. Why This Even Matters — A Story First A café has

Question 8

What is keep-alive in Vue?

Accepted Answer

**Target Audience:** Developers who know components and [dynamic components](/interview-question/how-do-dynamic-components-work) and want to keep state across switches. **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 hook log and warning below was produced by compiling and mounting the code on Vue 3.5.44 in jsdom with the repo's ver

Question 9

How do you fetch data in a Vue component (loading, errors, cancellation)?

Accepted Answer

**Target Audience:** Anyone preparing for a Vue interview who knows [watch and watchEffect](/interview-question/what-is-the-difference-between-watch-and-watcheffect) and basic fetch — no data-fetching library 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. All output was produced on Vue 3.5.44. **No real network was used*

Question 10

What are composables in Vue?

Accepted Answer

**Target Audience:** Vue developers who know `ref` and `computed` and want to reuse logic properly.
**Difficulty:** Medium

> **How to read this doc:** Plain language first, then `📌 Interview term:` callouts. Every output in the "Verified" sections was produced by running the examples on Vue 3.5.44: the SFC was compiled and mounted in jsdom with the repo verifier, the plain-JavaScript example ran under Node.

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

Think of a power tool battery. You do not

VUE.JSDECODED.

Easy

How do defineProps and defineEmits work in <script setup>?

Medium

How does Vue's reactivity system work?

What is the difference between watch and watchEffect?

How do dynamic routes and route params work in Vue Router?

What are provide and inject?

How do you handle errors in Vue (onErrorCaptured, app.config.errorHandler)?

What is the difference between computed and watch?

What is keep-alive in Vue?

How do you fetch data in a Vue component (loading, errors, cancellation)?

Hard

What is effectScope?

What is async setup and top-level await?

What are common reactivity caveats in Vue?

What is effectScope() and why do composables use it for cleanup?