rsnext/errors/invalid-use-server-value.mdx

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fix: Add stricter check for "use server" exports (#62821) As mentioned in the new-added error messages, and the [linked resources](https://react.dev/reference/react/use-server#:~:text=Because%20the%20underlying%20network%20calls%20are%20always%20asynchronous%2C%20%27use%20server%27%20can%20only%20be%20used%20on%20async%20functions.): > Because the underlying network calls are always asynchronous, 'use server' can only be used on async functions. > https://react.dev/reference/react/use-server It's a requirement that only async functions are allowed to be exported and annotated with `'use server'`. Currently, we already have compiler check so this will already error: ```js 'use server' export function foo () {} // missing async ``` However, since exported values can be very dynamic the compiler can't catch all mistakes like that. We also have a runtime check for all exports in a `'use server'` function, but it only covers `typeof value === 'function'`. This PR adds a stricter check for "use server" annotated values to also make sure they're async functions (`value.constructor.name === 'AsyncFunction'`). That said, there are still cases like synchronously returning a promise to make a function "async", but it's still very different by definition. For example: ```js const f = async () => { throw 1; return 1 } const g = () => { throw 1; return Promise.resolve(1) } ``` Where `g()` can be synchronously caught (`try { g() } catch {}`) but `f()` can't even if they have the same types. If we allow `g` to be a Server Action, this behavior is no longer always true but depending on where it's called (server or client). Closes #62727.
2024-03-04 18:50:19 +01:00
---
title: 'Invalid "use server" Value'
---
## Why This Error Occurred
This error occurs when a `"use server"` file exports a value that is not an async function. It might happen when you unintentionally export something like a configuration object, an arbitrary value, or missed the `async` keyword in the exported function declaration.
These functions are required to be defined as async, because `"use server"` marks them as [Server Actions](https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions-and-mutations) and they can be invoked directly from the client through a network request.
Examples of incorrect code:
```js
'use server'
// ❌ This is incorrect: only async functions are allowed.
export const value = 1
// ❌ This is incorrect: missed the `async` keyword.
export function getServerData() {
return '...'
}
```
Correct code:
```js
'use server'
// ✅ This is correct: an async function is exported.
export async function getServerData() {
return '...'
}
```
## Possible Ways to Fix It
Check all exported values in the `"use server"` file (including `export *`) and make sure that they are all defined as async functions.
## Useful Links
- [Server Actions and Mutations - Next.js](https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions-and-mutations)
- ['use server' directive - React](https://react.dev/reference/react/use-server)