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87 lines
2.5 KiB
Markdown
87 lines
2.5 KiB
Markdown
---
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navigation.icon: uil:database
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description: Nuxt provides useState composable to create a reactive and SSR-friendly shared state.
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---
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# State Management
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Nuxt provides useState composable to create a reactive and SSR-friendly shared state across components.
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`useState` 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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::ReadMore{link="/docs/api/composables/use-state"}
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::
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::alert{icon=👉}
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`useState` only works during `setup` or [`Lifecycle Hooks`](https://vuejs.org/api/composition-api-lifecycle.html#composition-api-lifecycle-hooks).
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::
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::alert{type=warning}
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Because the data inside `useState` 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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## Best Practices
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::alert{type=danger icon=🚨}
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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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::alert{type=success icon=✅}
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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 [app.vue]
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<script setup>
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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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::LinkExample{link="/docs/examples/composables/use-state"}
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::
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::ReadMore{link="/docs/api/composables/use-state"}
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::
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### Advanced
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In this example, we use a composable that detects the user's default locale from the HTTP request headers and keeps it in a `locale` state.
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::LinkExample{link="/docs/examples/other/locale"}
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::
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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 [composables/states.ts]
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export const useCounter = () => useState<number>('counter', () => 0)
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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>
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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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