Nuxt/docs/3.api/2.composables/use-state.md

---
title: "useState"
description: The useState composable creates a reactive and SSR-friendly shared state.
links:
  - label: Source
    icon: i-simple-icons-github
    to: https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/state.ts
    size: xs
---

## Usage

```ts
// Create a reactive state and set default value
const count = useState('counter', () => Math.round(Math.random() * 100))
```

:read-more{to="/docs/getting-started/state-management"}

::important
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.
::

::warning
`useState` is a reserved function name transformed by the compiler, so you should not name your own function `useState`.
::

::tip{icon="i-ph-video" to="https://www.youtube.com/watch?v=mv0WcBABcIk" target="_blank"}
Watch a video from Alexander Lichter about why and when to use `useState()`.
::

## Using `shallowRef`

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.

```ts
const state = useState('my-shallow-state', () => shallowRef({ deep: 'not reactive' }))
// isShallow(state) === true
```

## Type

```ts
useState<T>(init?: () => T | Ref<T>): Ref<T>
useState<T>(key: string, init?: () => T | Ref<T>): Ref<T>
```

- `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.
- `init`: A function that provides initial value for the state when not initiated. This function can also return a `Ref`.
- `T`: (typescript only) Specify the type of state