mirror of
https://github.com/nuxt/nuxt.git
synced 2024-11-11 16:43:55 +00:00
81 lines
2.5 KiB
Markdown
81 lines
2.5 KiB
Markdown
# State
|
|
|
|
Nuxt provides `useState` composable to create a reactive and SSR-friendly shared state across components.
|
|
|
|
`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.
|
|
|
|
## Signature
|
|
|
|
```ts
|
|
useState<T>(key: string, init?: () => T): Ref<T>
|
|
```
|
|
|
|
* **key**: A unique key ensuring that data fetching can be properly de-duplicated across requests
|
|
* **init**: A function that provides initial value for the state when it's not initiated
|
|
* **T**: (typescript only) Specify the type of state
|
|
|
|
::alert{icon=👉}
|
|
`useState` only works during `setup` or [`Lifecycle Hooks`](https://vuejs.org/api/composition-api-lifecycle.html#composition-api-lifecycle-hooks).
|
|
::
|
|
|
|
## Best practices
|
|
|
|
::alert{type=danger icon=🚨}
|
|
Never define `const state = ref()` outside of `<script setup>` or `setup()` function.<br>
|
|
Such state will be shared across all users visiting your website and can lead to memory leaks!
|
|
::
|
|
::alert{type=success icon=✅}
|
|
Instead use `const useX = () => useState('x')`
|
|
::
|
|
|
|
## Examples
|
|
|
|
### Basic usage
|
|
|
|
In this example, we use a component-local counter state. Any other component that uses `useState('counter')` shares the same reactive state.
|
|
|
|
```vue [app.vue]
|
|
<script setup>
|
|
const counter = useState('counter', () => Math.round(Math.random() * 1000))
|
|
</script>
|
|
|
|
<template>
|
|
<div>
|
|
Counter: {{ counter }}
|
|
<button @click="counter++">
|
|
+
|
|
</button>
|
|
<button @click="counter--">
|
|
-
|
|
</button>
|
|
</div>
|
|
</template>
|
|
```
|
|
|
|
:button-link[Open on StackBlitz]{href="https://stackblitz.com/github/nuxt/framework/tree/main/examples/use-state?terminal=dev" blank}
|
|
|
|
### Advanced
|
|
|
|
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.
|
|
|
|
:button-link[Open on StackBlitz]{href="https://stackblitz.com/github/nuxt/framework/tree/main/examples/locale?terminal=dev" blank}
|
|
|
|
## Shared state
|
|
|
|
By using [auto-imported composables](/docs/directory-structure/composables) we can define global type-safe states and import them across the app.
|
|
|
|
```ts [composables/states.ts]
|
|
export const useCounter = () => useState<number>('counter', () => 0)
|
|
export const useColor = () => useState<string>('color', () => 'pink')
|
|
```
|
|
|
|
```vue [app.vue]
|
|
<script setup>
|
|
const color = useColor() // Same as useState('color')
|
|
</script>
|
|
|
|
<template>
|
|
<p>Current color: {{ color }}</p>
|
|
</template>
|
|
```
|