Nuxt/docs/content/3.docs/1.usage/2.state.md

State

Nuxt provides useState to create a globally shared state within the context.

useState is SSR-friendly ref replacement in that its value will be hydrated (preserved) after server-side rendering and is shared across all components using a unique key.

::alert{icon=⚠️} Never define const state = ref() outside of <script setup> or setup() function. Such state will be shared across all users visiting your website and can lead to memory leaks!

✅ Instead use const useX = () => useState('x') ::

Usage

Within your pages, components and plugins you can use useState.

const state = 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 type of state

::alert{icon=👉} useState only works during setup or Lifecycle Hooks ::

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.

<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 Example

In this example, we use a composable that detects the user's default locale 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 we can define global type-safe states and import them across the app.

export const useCounter = () => useState<number>('counter', () => 0)
export const useColor = () => useState<string>('color', () => 'pink')

<script setup>
const color = useColor() // Same as useState('color')
</script>

<template>
  Current color: {{ color }}
</template>