vue-patterns

# Vue.js Patterns and Best Practices Comprehensive guide for Vue.js 3 development using Composition API (`<script setup>`), covering component design, reactivity, state management, routing, testing, and SSR patterns. Nuxt-specific guidance is included where it differs from vanilla Vue. ## When to Activate Activate this skill when: - The project uses Vue.js (any version), Nuxt, Vite + Vue, or Pinia. - The user asks about Vue component architecture, composables, reactivity, or state management. - Reviewing Vue Single-File Components (`.vue` files). - Setting up Vue Router, Pinia stores, or Vite/Vitest configuration. - Discussing Vue-specific performance, security, or SSR patterns. --- ## 1. Project Structure ### Recommended Layout (Feature-First) ``` src/ ├── api/ # API client and endpoint definitions ├── assets/ # Static assets (images, fonts, icons) ├── components/ # Shared/reusable components │ ├── base/ # Base UI primitives (Button, Input, Modal) │ └── features/ # Feature-specific shared components ├── composables/ # Reusable Composition API logic ├── layouts/ # Page layouts (optional) ├── pages/ # Route-level page components ├── router/ # Vue Router configuration ├── stores/ # Pinia stores ├── types/ # TypeScript type definitions ├── utils/ # Pure utility functions └── App.vue # Root component ``` ### File Naming | Convention | When to Use | |-----------|-------------| | `PascalCase.vue` | All components (enforced by `vue/multi-word-component-names`) | | `useCamelCase.ts` | Composables | | `camelCase.ts` | Utilities, API clients, types | | `kebab-case` directories | Route segments, feature folders | --- ## 2. Component Architecture ### Single-File Component Order ```vue <script setup lang="ts"> // 1. Imports (vue → ecosystem → absolute → relative) // 2. Props & Emits & Slots // 3. Composables // 4. Local state (ref/reactive) // 5. Computed properties // 6. Methods // 7. Watchers // 8. Lifecycle hooks </script> <template> <!-- Template content --> </template> <style scoped> /* Scoped styles */ </style> ``` ### Presentational vs Container - **Container components**: Own data fetching, state, and side effects. Render presentational components. - **Presentational components**: Receive props, emit events. No API calls, no store access. Pure rendering. ### Props Best Practices ```ts // Type-based props with defaults interface Props { label: string; variant?: "primary" | "secondary"; disabled?: boolean; items: Item[]; } const props = withDefaults(defineProps<Props>(), { variant: "primary", disabled: false, }); ``` - Always provide `type`, and `required`/`default` where appropriate. - Boolean props: `isXxx`, `hasXxx`, `canXxx`. - Never mutate props — emit events instead. - For v-model binding, use `defineModel()` (Vue 3.4+) or `modelValue` + `update:modelValue`. ### Events ```ts const emit = defineEmits<{ submit: []; "update:modelValue": [value: string]; select: [id: string, index: number]; }>(); ``` - Use kebab-case in templates (`@update:model-value`). - Use camelCase in script (`emit("update:modelValue", val)`). --- ## 3. Composables (Reusable Logic) ### Structure ```ts // composables/useDebounce.ts export function useDebounce<T>(value: MaybeRef<T>, delay: number): Ref<T> { const debounced = ref(toValue(value)) as Ref<T>; let timer: ReturnType<typeof setTimeout>; watch( () => toValue(value), (newVal) => { clearTimeout(timer); timer = setTimeout(() => { debounced.value = newVal; }, delay); } ); onUnmounted(() => clearTimeout(timer)); return readonly(debounced); } ``` ### Rules - Must start with `use` prefix. - Return reactive values (`ref`, `computed`, `reactive`), never plain primitives. - Accept reactive inputs via `MaybeRef` / `toRef()` / `toValue()`. - Clean up side effects in `onUnmounted` or watcher `onCleanup`. - No module-scope side effects. ### vs Mixins Composables replace Vue 2 mixins entirely: - **Mixins**: Opaque data flow, source-of-truth collisions, name conflicts. - **Composables**: Explicit imports, clear return values, composable and tree-shakable. --- ## 4. State Management ### When to Use What | Pattern | Use Case | |---------|----------| | `ref()` / `reactive()` | Local component state | | Props + Emits | Parent-child communication | | Provide / Inject | Theme, config, plugin API | | Pinia store | Global, shared, complex state | | Server state composable | API data with caching (wrap `fetch`/TanStack Query) | ### Pinia Setup Store (Preferred) ```ts // stores/useCartStore.ts export const useCartStore = defineStore("cart", () => { const items = ref<CartItem[]>([]); const isLoading = ref(false); const totalPrice = computed(() => items.value.reduce((sum, i) => sum + i.price * i.quantity, 0) ); const itemCount = computed(() => items.value.reduce((sum, i) => sum + i.quantity, 0) ); async function addItem(productId: string) { isLoading.value = true; try { const item = await fetchProduct(productId); const existing = items.value.find(i => i.id === item.id); if (existing) existing.quantity++; else items.value.push({ ...item, quantity: 1 }); } finally { isLoading.value = false; } } return { items, isLoading, totalPrice, itemCount, addItem }; }); ``` - Use Setup Store syntax (not Options Store). - Prefer actions for business-level mutations and `$patch()` for grouped updates. - Every async action: handle loading + success + error. --- ## 5. Vue Router ### Route Definitions ```ts const routes = [ { path: "/users/:id", name: "user-detail", component: () => import("@/pages/UserDetail.vue"), // lazy props: true, // pass params as props meta: { requiresAuth: true }, }, ]; ``` ### Navigation Guards ```ts router.beforeEach((to, from) => { const { isLoggedIn } = useAuthStore(); if (to.meta.requiresAuth && !isLoggedIn) { return { name: "login", query: { redirect: to.fullPath } }; } }); ``` ### Reactive Route Params When a component stays mounted but route params change: ```ts const route = useRoute(); const id = computed(() => route.params.id as string); watch(id, (newId) => fetchItem(newId)); ``` --- ## 6. Template Patterns ### Template Syntax ```vue <!-- v-if/v-else-if/v-else --> <div v-if="isLoading">Loading...</div> <div v-else-if="error">Error: {{ error }}</div> <div v-else>{{ content }}</div> <!-- v-show for frequent toggles --> <div v-show="isOpen">Toggled content</div> <!-- v-for with stable keys --> <div v-for="item in items" :key="item.id">{{ item.name }}</div> <!-- Computed filtered list (not v-if + v-for on same element) --> <div v-for="item in activeItems" :key="item.id">{{ item.name }}</div> <!-- Event handling --> <form @submit.prevent="handleSubmit"> <button type="submit">Save</button> </form> <!-- v-model --> <input v-model="name" /> <CustomInput v-model="value" v-model:title="title" /> ``` --- ## 7. Performance | Technique | When to Use | |-----------|-------------| | `v-memo` | List items that rarely change | | `v-once` | Content rendered once and static forever | | `shallowRef()` | Large data structures replaced wholesale | | `shallowReactive()` | Only top-level properties are reactive | | `v-show` over `v-if` | Frequent visibility toggles | | `<KeepAlive :max="10">` | Cache toggled views | | Lazy routes | `() => import(...)` for non-critical routes | | `Suspense` | Async component loading with fallback | --- ## 8. Testing ### Stack - **Vitest** for unit and component tests - **Vue Test Utils** for mounting and interaction - **@pinia/testing** for store mocking - **Playwright** for E2E ### Component Test Pattern ```ts import { mount } from "@vue/test-utils"; import { createPinia, setActivePinia } from "pinia"; import UserCard from "./UserCard.vue"; beforeEach(() => { setActivePinia(createPinia()); }); it("renders and emits", async () => { const wrapper = mount(UserCard, { props: { user: { id: "1", name: "Alice" } }, }); expect(wrapper.text()).toContain("Alice"); await wrapper.find("button").trigger("click"); expect(wrapper.emitted("select")![0]).toEqual(["1"]); }); ``` --- ## 9. Nuxt-Specific Patterns ### Auto-Imports Nuxt auto-imports `ref`, `computed`, `watch`, `useFetch`, `useAsyncData`, etc. Use them directly without importing. For non-Nuxt projects, always import explicitly. ### useAsyncData / useFetch ```ts const { data: user, pending, error, refresh } = await useAsyncData( "user", // unique key for caching () => $fetch(`/api/users/${id}`), ); const { data: posts } = await useFetch("/api/posts", { query: { page: 1 }, key: "posts-page-1", // dedupes requests }); ``` ### Server Routes ```ts // server/api/users/[id].ts export default defineEventHandler(async (event) => { const { id } = await getValidatedRouterParams(event, z.object({ id: z.string().uuid(), }).parse); // ... fetch and return }); ``` ### Runtime Config ```ts // nuxt.config.ts export default defineNuxtConfig({ runtimeConfig: { // server-only apiSecret: "", // public (exposed to client) public: { apiBase: "https://api.example.com", }, }, }); ``` --- ## 10. Vue 3.5+ New APIs ### Reactive Props Destructure Vue 3.5 stabilized reactive props destructure — destructured variables from `defineProps()` are automatically reactive: ```ts // Vue 3.5+: destructured props are reactive (no need for toRefs)