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61 lines
2.1 KiB
Markdown
61 lines
2.1 KiB
Markdown
---
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title: "callOnce"
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description: "Run a given function or block of code once during SSR or CSR."
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navigation:
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badge: New
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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/once.ts
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size: xs
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---
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::callout{icon="i-ph-info-duotone" color="blue"}
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This utility is available since [Nuxt v3.9](/blog/v3-9).
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::
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## Purpose
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The `callOnce` function is designed to execute a given function or block of code only once during:
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- server-side rendering but not hydration
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- client-side navigation
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This is useful for code that should be executed only once, such as logging an event or setting up a global state.
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## Usage
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```vue [app.vue]
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<script setup lang="ts">
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const websiteConfig = useState('config')
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await callOnce(async () => {
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console.log('This will only be logged once')
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websiteConfig.value = await $fetch('https://my-cms.com/api/website-config')
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})
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</script>
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```
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::callout{to="/docs/getting-started/state-management#usage-with-pinia"}
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`callOnce` is useful in combination with the [Pinia module](/modules/pinia) to call store actions.
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::
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:read-more{to="/docs/getting-started/state-management"}
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::callout{color="info" icon="i-ph-warning-duotone"}
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Note that `callOnce` doesn't return anything. You should use [`useAsyncData`](/docs/api/composables/use-async-data) or [`useFetch`](/docs/api/composables/use-fetch) if you want to do data fetching during SSR.
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::
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::callout
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`callOnce` is a composable meant to be called directly in a setup function, plugin, or route middleware, because it needs to add data to the Nuxt payload to avoid re-calling the function on the client when the page hydrates.
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::
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## Type
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```ts
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callOnce(fn?: () => any | Promise<any>): Promise<void>
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callOnce(key: string, fn?: () => any | Promise<any>): Promise<void>
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```
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- `key`: A unique key ensuring that the code is run once. If you do not provide a key, then a key that is unique to the file and line number of the instance of `callOnce` will be generated for you.
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- `fn`: The function to run once. This function can also return a `Promise` and a value.
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