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220 lines
6.3 KiB
Markdown
220 lines
6.3 KiB
Markdown
---
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title: 'State Management'
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description: Nuxt provides powerful state management libraries and the useState composable to create a reactive and SSR-friendly shared state.
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navigation.icon: i-ph-database-duotone
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---
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Nuxt provides the [`useState`](/docs/api/composables/use-state) composable to create a reactive and SSR-friendly shared state across components.
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[`useState`](/docs/api/composables/use-state) is an SSR-friendly [`ref`](https://vuejs.org/api/reactivity-core.html#ref) replacement. Its value will be preserved after server-side rendering (during client-side hydration) and shared across all components using a unique key.
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::important
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Because the data inside [`useState`](/docs/api/composables/use-state) will be serialized to JSON, it is important that it does not contain anything that cannot be serialized, such as classes, functions or symbols.
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::
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::read-more{to="/docs/api/composables/use-state"}
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Read more about `useState` composable.
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::
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## Best Practices
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::warning
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Never define `const state = ref()` outside of `<script setup>` or `setup()` function.<br>
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Such state will be shared across all users visiting your website and can lead to memory leaks!
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::
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::tip{icon="i-ph-check-circle-duotone"}
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Instead use `const useX = () => useState('x')`
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::
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## Examples
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### Basic Usage
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In this example, we use a component-local counter state. Any other component that uses `useState('counter')` shares the same reactive state.
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```vue twoslash [app.vue]
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<script setup lang="ts">
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const counter = useState('counter', () => Math.round(Math.random() * 1000))
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</script>
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<template>
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<div>
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Counter: {{ counter }}
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<button @click="counter++">
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+
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</button>
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<button @click="counter--">
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-
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</button>
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</div>
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</template>
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```
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:link-example{to="/docs/examples/features/state-management"}
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::note
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To globally invalidate cached state, see [`clearNuxtState`](/docs/api/utils/clear-nuxt-state) util.
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::
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### Initializing State
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Most of the time, you will want to initialize your state with data that resolves asynchronously. You can use the [`app.vue`](/docs/guide/directory-structure/app) component with the [`callOnce`](/docs/api/utils/call-once) util to do so.
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```vue twoslash [app.vue]
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<script setup lang="ts">
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const websiteConfig = useState('config')
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await callOnce(async () => {
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websiteConfig.value = await $fetch('https://my-cms.com/api/website-config')
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})
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</script>
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```
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::tip
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This is similar to the [`nuxtServerInit` action](https://v2.nuxt.com/docs/directory-structure/store/#the-nuxtserverinit-action) in Nuxt 2, which allows filling the initial state of your store server-side before rendering the page.
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::
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:read-more{to="/docs/api/utils/call-once"}
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### Usage with Pinia
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In this example, we leverage the [Pinia module](/modules/pinia) to create a global store and use it across the app.
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::important
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Make sure to install the Pinia module with `npx nuxi@latest module add pinia` or follow the [module's installation steps](https://pinia.vuejs.org/ssr/nuxt.html#Installation).
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::
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::code-group
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```ts [stores/website.ts]
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export const useWebsiteStore = defineStore('websiteStore', {
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state: () => ({
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name: '',
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description: ''
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}),
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actions: {
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async fetch() {
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const infos = await $fetch('https://api.nuxt.com/modules/pinia')
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this.name = infos.name
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this.description = infos.description
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}
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}
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})
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```
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```vue [app.vue]
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<script setup lang="ts">
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const website = useWebsiteStore()
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await callOnce(website.fetch)
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</script>
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<template>
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<main>
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<h1>{{ website.name }}</h1>
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<p>{{ website.description }}</p>
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</main>
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</template>
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```
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::
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## Advanced Usage
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::code-group
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```ts [composables/locale.ts]
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import type { Ref } from 'vue'
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export const useLocale = () => {
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return useState<string>('locale', () => useDefaultLocale().value)
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}
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export const useDefaultLocale = (fallback = 'en-US') => {
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const locale = ref(fallback)
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if (import.meta.server) {
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const reqLocale = useRequestHeaders()['accept-language']?.split(',')[0]
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if (reqLocale) {
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locale.value = reqLocale
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}
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} else if (import.meta.client) {
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const navLang = navigator.language
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if (navLang) {
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locale.value = navLang
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}
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}
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return locale
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}
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export const useLocales = () => {
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const locale = useLocale()
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const locales = ref([
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'en-US',
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'en-GB',
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...
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'ja-JP-u-ca-japanese'
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])
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if (!locales.value.includes(locale.value)) {
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locales.value.unshift(locale.value)
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}
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return locales
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}
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export const useLocaleDate = (date: Ref<Date> | Date, locale = useLocale()) => {
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return computed(() => new Intl.DateTimeFormat(locale.value, { dateStyle: 'full' }).format(unref(date)))
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}
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```
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```vue [app.vue]
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<script setup lang="ts">
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const locales = useLocales()
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const locale = useLocale()
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const date = useLocaleDate(new Date('2016-10-26'))
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</script>
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<template>
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<div>
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<h1>Nuxt birthday</h1>
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<p>{{ date }}</p>
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<label for="locale-chooser">Preview a different locale</label>
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<select id="locale-chooser" v-model="locale">
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<option v-for="locale of locales" :key="locale" :value="locale">
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{{ locale }}
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</option>
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</select>
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</div>
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</template>
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```
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::
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:link-example{to="/docs/examples/advanced/locale"}
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## Shared State
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By using [auto-imported composables](/docs/guide/directory-structure/composables) we can define global type-safe states and import them across the app.
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```ts twoslash [composables/states.ts]
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export const useColor = () => useState<string>('color', () => 'pink')
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```
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```vue [app.vue]
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<script setup lang="ts">
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// ---cut-start---
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const useColor = () => useState<string>('color', () => 'pink')
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// ---cut-end---
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const color = useColor() // Same as useState('color')
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</script>
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<template>
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<p>Current color: {{ color }}</p>
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</template>
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```
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## Using third-party libraries
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Nuxt **used to rely** on the Vuex library to provide global state management. If you are migrating from Nuxt 2, please head to [the migration guide](/docs/migration/configuration#vuex).
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Nuxt is not opinionated about state management, so feel free to choose the right solution for your needs. There are multiple integrations with the most popular state management libraries, including:
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- [Pinia](/modules/pinia) - the official Vue recommendation
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- [Harlem](/modules/harlem) - immutable global state management
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- [XState](/modules/xstate) - state machine approach with tools for visualizing and testing your state logic
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