Nuxt 4 Production Guide

Hydration, performance, testing, deployment, and migration patterns.

What's New in Nuxt 4 v4.2 Features (Latest)

1. Abort Control for Data Fetching

const controller = ref()

const { data } = await useAsyncData( 'users', () => $fetch('/api/users', { signal: controller.value?.signal }) )

const abortRequest = () => { controller.value?.abort() controller.value = new AbortController() }

1. Async Data Handler Extraction

39% smaller client bundles Data fetching logic extracted to server chunks Automatic optimization (no config needed)

1. Enhanced Error Handling

Dual error display: custom error page + technical overlay Better error messages in development v4.1 Features

1. Enhanced Chunk Stability

Import maps prevent cascading hash changes Better long-term caching

1. Lazy Hydration

Breaking Changes from v3 Change v3 v4 Source directory Root app/ Data reactivity Deep Shallow (default) Default values null undefined Route middleware Client Server App manifest Opt-in Default When to Load References

Load references/hydration.md when:

Debugging "Hydration node mismatch" errors Implementing ClientOnly components Fixing non-deterministic rendering issues Understanding SSR vs client rendering

Load references/performance.md when:

Optimizing Core Web Vitals scores Implementing lazy loading and code splitting Configuring caching strategies Reducing bundle size

Load references/testing-vitest.md when:

Writing component tests with @nuxt/test-utils Testing composables with Nuxt context Mocking Nuxt APIs (useFetch, useRoute) Setting up Vitest configuration

Load references/deployment-cloudflare.md when:

Deploying to Cloudflare Pages or Workers Configuring wrangler.toml Setting up NuxtHub integration Working with D1, KV, R2 bindings Hydration Best Practices What Causes Hydration Mismatches Cause Example Fix Non-deterministic values Math.random() Use useState Browser APIs on server window.innerWidth Use onMounted Date/time on server new Date() Use useState or ClientOnly Third-party scripts Analytics Use ClientOnly Fix Patterns

Non-deterministic Values:

Browser APIs:

ClientOnly Component:

Conditional Rendering:

Performance Optimization Lazy Loading Components

Lazy Hydration

Route Caching // nuxt.config.ts export default defineNuxtConfig({ routeRules: { // Static pages (prerendered at build) '/': { prerender: true }, '/about': { prerender: true },

// SWR caching (1 hour)
'/blog/**': { swr: 3600 },

// ISR (regenerate every hour)
'/products/**': { isr: 3600 },

// SPA mode (no SSR)
'/dashboard/**': { ssr: false },

// Static with CDN caching
'/static/**': {
  headers: { 'Cache-Control': 'public, max-age=31536000' }
}

} })

Image Optimization

Testing with Vitest Setup bun add -d @nuxt/test-utils vitest @vue/test-utils happy-dom

// vitest.config.ts import { defineVitestConfig } from '@nuxt/test-utils/config'

export default defineVitestConfig({ test: { environment: 'nuxt', environmentOptions: { nuxt: { domEnvironment: 'happy-dom' } } } })

Component Testing // tests/components/UserCard.test.ts import { describe, it, expect } from 'vitest' import { mountSuspended } from '@nuxt/test-utils/runtime' import UserCard from '~/components/UserCard.vue'

describe('UserCard', () => { it('renders user name', async () => { const wrapper = await mountSuspended(UserCard, { props: { user: { id: 1, name: 'John Doe', email: 'john@example.com' } } })

expect(wrapper.text()).toContain('John Doe')
expect(wrapper.text()).toContain('john@example.com')

})

it('emits delete event', async () => { const wrapper = await mountSuspended(UserCard, { props: { user: { id: 1, name: 'John' } } })

await wrapper.find('[data-test="delete-btn"]').trigger('click')

expect(wrapper.emitted('delete')).toHaveLength(1)
expect(wrapper.emitted('delete')[0]).toEqual([1])

}) })

Mocking Composables // tests/components/Dashboard.test.ts import { describe, it, expect, vi } from 'vitest' import { mountSuspended, mockNuxtImport } from '@nuxt/test-utils/runtime' import Dashboard from '~/pages/dashboard.vue'

// Mock useFetch mockNuxtImport('useFetch', () => { return () => ({ data: ref({ users: [{ id: 1, name: 'John' }] }), pending: ref(false), error: ref(null) }) })

describe('Dashboard', () => { it('displays users from API', async () => { const wrapper = await mountSuspended(Dashboard)

expect(wrapper.text()).toContain('John')

}) })

Testing Server Routes // tests/api/users.test.ts import { describe, it, expect } from 'vitest' import { $fetch, setup } from '@nuxt/test-utils/e2e'

describe('API: /api/users', async () => { await setup({ server: true })

it('returns users list', async () => { const users = await $fetch('/api/users')

expect(users).toHaveProperty('users')
expect(Array.isArray(users.users)).toBe(true)

})

it('creates a new user', async () => { const result = await $fetch('/api/users', { method: 'POST', body: { name: 'Jane', email: 'jane@example.com' } })

expect(result.user.name).toBe('Jane')

}) })

Deployment Cloudflare Pages (Recommended)

Build and deploy

bun run build bunx wrangler pages deploy .output/public

// nuxt.config.ts export default defineNuxtConfig({ nitro: { preset: 'cloudflare-pages' } })

Cloudflare Workers // nuxt.config.ts export default defineNuxtConfig({ nitro: { preset: 'cloudflare-module' } })

wrangler.toml

name = "my-nuxt-app" compatibility_date = "2025-01-01" compatibility_flags = ["nodejs_compat"]

[[ d1_databases ]] binding = "DB" database_name = "my-database" database_id = "xxx-xxx-xxx"

[[ kv_namespaces ]] binding = "KV" id = "xxx-xxx-xxx"

Vercel // nuxt.config.ts export default defineNuxtConfig({ nitro: { preset: 'vercel' } })

Netlify // nuxt.config.ts export default defineNuxtConfig({ nitro: { preset: 'netlify' } })

NuxtHub (Cloudflare All-in-One) bun add @nuxthub/core

// nuxt.config.ts export default defineNuxtConfig({ modules: ['@nuxthub/core'],

hub: { database: true, // D1 kv: true, // KV blob: true, // R2 cache: true // Cache API } })

// Usage in server routes export default defineEventHandler(async (event) => { const db = hubDatabase() const kv = hubKV() const blob = hubBlob()

// Use like regular Cloudflare bindings const users = await db.prepare('SELECT * FROM users').all() })

Environment Variables

.env (development)

API_SECRET=dev-secret DATABASE_URL=http://localhost:8787

Production (Cloudflare)

wrangler secret put API_SECRET wrangler secret put DATABASE_URL

Production (Vercel/Netlify)

Set in dashboard or CLI

Migration from Nuxt 3 Step 1: Update package.json { "devDependencies": { "nuxt": "^4.0.0" } }

Step 2: Enable Compatibility Mode // nuxt.config.ts export default defineNuxtConfig({ future: { compatibilityVersion: 4 } })

Step 3: Move Files to app/

Create app directory

mkdir app

Move files

mv components app/ mv composables app/ mv pages app/ mv layouts app/ mv middleware app/ mv plugins app/ mv assets app/ mv app.vue app/ mv error.vue app/

Step 4: Fix Shallow Reactivity // If mutating data.value properties: const { data } = await useFetch('/api/user', { deep: true // Enable deep reactivity })

// Or replace entire value data.value = { ...data.value, name: 'New Name' }

Step 5: Update Default Values // v3: data.value is null // v4: data.value is undefined

// Update null checks if (data.value === null) // v3 if (!data.value) // v4 (works for both)

Common Anti-Patterns Client-Only Code on Server // WRONG const width = window.innerWidth

// CORRECT if (import.meta.client) { const width = window.innerWidth }

// Or use onMounted onMounted(() => { const width = window.innerWidth })

Non-Deterministic SSR // WRONG - Different on server vs client const id = Math.random() const time = Date.now()

// CORRECT - Use useState for consistency const id = useState('id', () => Math.random()) const time = useState('time', () => Date.now())

Missing Suspense for Async Components

Troubleshooting

Hydration Mismatch:

Check for window, document, localStorage usage Wrap in ClientOnly or use onMounted Look for Math.random(), Date.now(), crypto.randomUUID()

Build Errors:

rm -rf .nuxt .output node_modules/.vite && bun install

Deployment Fails:

Check nitro.preset matches target Verify environment variables are set Check wrangler.toml bindings match code

Tests Failing:

Ensure @nuxt/test-utils is installed Check vitest.config.ts has environment: 'nuxt' Use mountSuspended for async components Related Skills nuxt-core: Project setup, routing, configuration nuxt-data: Composables, data fetching, state nuxt-server: Server routes, API patterns cloudflare-d1: D1 database patterns

Version: 4.0.0 | Last Updated: 2025-12-28 | License: MIT