Vue JS Vue JS Performance Optimization 2 — Questions and Answers
Question 1: What is the recommended approach to avoid expensive computations running on every render in Vue?
- Place the logic in a method
- Use computed() to cache the result until reactive dependencies change (Correct answer)
- Use a watcher with immediate: true
- Run the logic in onMounted() and store the result in data
Correct answer: Use computed() to cache the result until reactive dependencies change
computed properties are cached based on their reactive dependencies and only recalculate when a dependency changes, preventing redundant computation on every render.
Question 2: Which Vue DevTools feature helps identify which components are re-rendering unnecessarily?
- Network panel
- Component timeline / performance profiler (Correct answer)
- Vuex inspector
- Storage explorer
Correct answer: Component timeline / performance profiler
Vue DevTools' Performance tab / Timeline shows component render timings and highlights components that re-render, helping identify wasted renders.
Question 3: How can you defer rendering of off-screen or non-critical components to improve initial load in Vue?
- Use v-if with a flag set to true after onMounted()
- Use v-show to hide them
- Use v-once on all non-critical sections
- Use async components with defineAsyncComponent() (Correct answer)
Correct answer: Use async components with defineAsyncComponent()
defineAsyncComponent() creates a component that is only loaded from the server when it is first rendered, and can include loading/error states.
Question 4: What is the benefit of using functional components in Vue for performance-sensitive rendering?
- They have no reactive state or lifecycle hooks, making them lighter and faster to render (Correct answer)
- They bypass the virtual DOM entirely
- They run in a Web Worker thread
- They pre-compile templates at build time only
Correct answer: They have no reactive state or lifecycle hooks, making them lighter and faster to render
Functional components are stateless and instanceless, so Vue skips creating a component instance, reducing memory use and rendering overhead.
Question 5: Why should you avoid using v-if and v-for on the same element in Vue?
- It causes a syntax error
- v-if has higher priority in Vue 3, causing each iteration to re-evaluate the condition needlessly (Correct answer)
- v-for renders before v-if, creating all DOM nodes before hiding them
- Vue does not support combining these directives
Correct answer: v-if has higher priority in Vue 3, causing each iteration to re-evaluate the condition needlessly
In Vue 3 v-if takes priority over v-for, meaning the condition is checked before the list can be iterated; this is confusing and inefficient — use a computed array instead.
Question 6: What does the Vite build tool do during production builds to improve Vue application performance?
- Converts Vue SFCs to vanilla JavaScript files at runtime
- Tree-shakes unused code, minifies output, and code-splits dynamic imports into separate chunks (Correct answer)
- Compiles Vue templates on the client browser
- Replaces all API calls with cached responses
Correct answer: Tree-shakes unused code, minifies output, and code-splits dynamic imports into separate chunks
Vite's production build uses Rollup to eliminate dead code, minify JavaScript/CSS, and split dynamic imports into optimized chunks for faster loading.
Vue JS Vue JS Performance Optimization 2
What is the recommended approach to avoid expensive computations running on every render in Vue?