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Pulled ALL skills from 15 source repositories: - anthropics/skills: 16 (docs, design, MCP, testing) - obra/superpowers: 14 (TDD, debugging, agents, planning) - coreyhaines31/marketingskills: 25 (marketing, CRO, SEO, growth) - better-auth/skills: 5 (auth patterns) - vercel-labs/agent-skills: 5 (React, design, Vercel) - antfu/skills: 16 (Vue, Vite, Vitest, pnpm, Turborepo) - Plus 13 individual skills from various repos Mosaic Stack is not limited to coding — the Orchestrator and subagents serve coding, business, design, marketing, writing, logistics, analysis, and more. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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skills/vue-best-practices/reference/updated-hook-performance.md
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skills/vue-best-practices/reference/updated-hook-performance.md
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---
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title: Avoid Expensive Operations in Updated Hook
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impact: MEDIUM
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impactDescription: Heavy computations in updated hook cause performance bottlenecks and potential infinite loops
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type: capability
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tags: [vue3, vue2, lifecycle, updated, performance, optimization, reactivity]
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---
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# Avoid Expensive Operations in Updated Hook
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**Impact: MEDIUM** - The `updated` hook runs after every reactive state change that causes a re-render. Placing expensive operations, API calls, or state mutations here can cause severe performance degradation, infinite loops, and dropped frames below the optimal 60fps threshold.
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Use `updated`/`onUpdated` sparingly for post-DOM-update operations that cannot be handled by watchers or computed properties. For most reactive data handling, prefer watchers (`watch`/`watchEffect`) which provide more control over what triggers the callback.
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## Task Checklist
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- [ ] Never perform API calls in updated hook
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- [ ] Never mutate reactive state inside updated (causes infinite loops)
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- [ ] Use conditional checks to verify updates are relevant before acting
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- [ ] Prefer `watch` or `watchEffect` for reacting to specific data changes
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- [ ] Use throttling/debouncing if updated operations are expensive
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- [ ] Reserve updated for low-level DOM synchronization tasks
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**Incorrect:**
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```javascript
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// WRONG: API call in updated - fires on EVERY re-render
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export default {
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data() {
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return { items: [], lastUpdate: null }
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},
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updated() {
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// This runs after every single state change!
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fetch('/api/sync', {
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method: 'POST',
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body: JSON.stringify(this.items)
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})
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}
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}
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```
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```javascript
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// WRONG: State mutation in updated - INFINITE LOOP
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export default {
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data() {
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return { renderCount: 0 }
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},
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updated() {
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// This causes another update, which triggers updated again!
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this.renderCount++ // INFINITE LOOP!
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}
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}
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```
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```javascript
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// WRONG: Heavy computation on every update
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export default {
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updated() {
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// Expensive operation runs on every keystroke, every state change
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this.processedData = this.heavyComputation(this.rawData)
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this.analytics = this.calculateMetrics(this.allData)
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}
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}
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```
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**Correct:**
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```javascript
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// CORRECT: Use watcher for specific data changes
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export default {
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data() {
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return { items: [] }
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},
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watch: {
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// Only fires when items actually changes
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items: {
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handler(newItems) {
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this.syncToServer(newItems)
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},
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deep: true
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}
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},
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methods: {
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syncToServer: debounce(function(items) {
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fetch('/api/sync', {
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method: 'POST',
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body: JSON.stringify(items)
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})
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}, 500)
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}
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}
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```
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```vue
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<!-- CORRECT: Composition API with targeted watchers -->
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<script setup>
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import { ref, watch, onUpdated } from 'vue'
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import { useDebounceFn } from '@vueuse/core'
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const items = ref([])
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const scrollContainer = ref(null)
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// Watch specific data - not all updates
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watch(items, (newItems) => {
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syncToServer(newItems)
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}, { deep: true })
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const syncToServer = useDebounceFn((items) => {
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fetch('/api/sync', { method: 'POST', body: JSON.stringify(items) })
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}, 500)
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// Only use onUpdated for DOM synchronization
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onUpdated(() => {
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// Scroll to bottom only if content changed height
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if (scrollContainer.value) {
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scrollContainer.value.scrollTop = scrollContainer.value.scrollHeight
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}
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})
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</script>
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```
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```javascript
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// CORRECT: Conditional check in updated hook
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export default {
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data() {
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return {
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content: '',
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lastSyncedContent: ''
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}
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},
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updated() {
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// Only act if specific condition is met
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if (this.content !== this.lastSyncedContent) {
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this.syncContent()
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this.lastSyncedContent = this.content
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}
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},
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methods: {
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syncContent: debounce(function() {
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// Sync logic
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}, 300)
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}
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}
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```
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## Valid Use Cases for Updated Hook
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```javascript
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// CORRECT: Low-level DOM synchronization
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export default {
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updated() {
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// Sync third-party library with Vue's DOM
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this.thirdPartyWidget.refresh()
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// Update scroll position after content change
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this.$nextTick(() => {
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this.maintainScrollPosition()
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})
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}
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}
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```
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## Prefer Computed Properties for Derived Data
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```javascript
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// WRONG: Calculating derived data in updated
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export default {
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data() {
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return { numbers: [1, 2, 3, 4, 5] }
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},
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updated() {
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this.sum = this.numbers.reduce((a, b) => a + b, 0) // Causes another update!
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}
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}
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// CORRECT: Use computed property instead
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export default {
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data() {
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return { numbers: [1, 2, 3, 4, 5] }
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},
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computed: {
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sum() {
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return this.numbers.reduce((a, b) => a + b, 0)
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}
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}
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}
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```
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## Reference
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- [Vue.js Lifecycle Hooks](https://vuejs.org/guide/essentials/lifecycle.html)
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- [Vue.js Watchers](https://vuejs.org/guide/essentials/watchers.html)
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- [Vue.js Computed Properties](https://vuejs.org/guide/essentials/computed.html)
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