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48 lines
1.8 KiB
Markdown
48 lines
1.8 KiB
Markdown
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---
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title: "useState"
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description: The useState composable creates a reactive and SSR-friendly shared state.
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links:
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- label: Source
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icon: i-simple-icons-github
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to: https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/state.ts
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size: xs
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---
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## Usage
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```ts
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// Create a reactive state and set default value
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const count = useState('counter', () => Math.round(Math.random() * 100))
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```
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:read-more{to="/docs/getting-started/state-management"}
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::callout
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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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::callout{color="amber" icon="i-ph-warning-duotone"}
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`useState` is a reserved function name transformed by the compiler, so you should not name your own function `useState`.
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::
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## Using `shallowRef`
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If you don't need your state to be deeply reactive, you can combine `useState` with [`shallowRef`](https://vuejs.org/api/reactivity-advanced.html#shallowref). This can improve performance when your state contains large objects and arrays.
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```ts
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const state = useState('my-shallow-state', () => shallowRef({ deep: 'not reactive' }))
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// isShallow(state) === true
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```
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## Type
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```ts
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useState<T>(init?: () => T | Ref<T>): Ref<T>
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useState<T>(key: string, init?: () => T | Ref<T>): Ref<T>
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```
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- `key`: A unique key ensuring that data fetching is properly de-duplicated across requests. If you do not provide a key, then a key that is unique to the file and line number of the instance of [`useState`](/docs/api/composables/use-state) will be generated for you.
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- `init`: A function that provides initial value for the state when not initiated. This function can also return a `Ref`.
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- `T`: (typescript only) Specify the type of state
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