Q: How does Vue's virtual DOM diff keyed lists?

**Target Audience:** Vue developers who use v-for with :key every day and want to explain what the renderer actually does with those keys. **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 DOM-operation counts in section 6 come from mounting lists with Vue 3.5.44 in jsdom and wrapping insertBefore , r

Question 1

What are v-once and v-memo?

Accepted Answer

**Target Audience:** Vue developers optimising rendering, and anyone asked how Vue templates compile. **Difficulty:** Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The compiled render functions below were printed by compile() from @vue/compiler-dom and @vue/compiler-ssr 3.5.44 (the import lines are trimmed); render counts and behaviour come from mounting the SFCs in jsdom with the repo verifier. For t

Question 2

When should you choose Vapor over VDOM in a real app — trade-offs?

Accepted Answer

**Target Audience:** Senior Vue developers and tech leads deciding whether and where to adopt Vapor mode. Assumes you know what Vapor is; if not, read [What is Vapor mode](/interview-question/what-is-vapor-mode-in-vue-3-5-and-how-does-it-differ-from-the-virtual-dom) first. **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. All numbers here were meas

Question 3

How do you render very large lists efficiently in Vue (virtual scrolling)?

Accepted Answer

**Target Audience:** Vue developers who have hit a slow page with a long list and want to explain or build virtual scrolling. Assumes v-for and computed. **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 runnable list passed scripts/verify-vue-example.mjs on Vue 3.5.44 (mounted in jsdom, scrolled by settin

Question 4

How does Vue's virtual DOM diff keyed lists?

Accepted Answer

**Target Audience:** Vue developers who use v-for with :key every day and want to explain what the renderer actually does with those keys. **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 DOM-operation counts in section 6 come from mounting lists with Vue 3.5.44 in jsdom and wrapping insertBefore, r

Question 5

What is a custom renderer in Vue (createRenderer)?

Accepted Answer

**Target Audience:** Vue developers curious about how Vue is structured internally, or evaluating Vue for a non-DOM target (canvas, 3D, terminal, native). **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 runnable example passed scripts/verify-vue-example.mjs on Vue 3.5.44 (compiled and mounted in jsdom, button clicked). The termin

VUE.JSDECODED.

Hard

What are v-once and v-memo?

When should you choose Vapor over VDOM in a real app — trade-offs?

How do you render very large lists efficiently in Vue (virtual scrolling)?

How does Vue's virtual DOM diff keyed lists?

What is a custom renderer in Vue (createRenderer)?