Why do I encounter "server actions that must be asynchronous functions" ?

[FatNerdPeng]

Summary

Hello, everyone, I'm new next.js and react,I encountered a problem that may be low-level but I have been unable to understand like this. I worte a log.ts to record all error in front-end by send request to backend

'use server';

import { RequestMethods } from './request';

// 日志级别
export enum LogLevels {
  Info = 'INFO',
  Warn = 'WARN',
  Error = 'ERROR',
}

export type A = {
  a: string;
};

/**
 * 这个方法不调用httpRequest,因为触发这个函数,会执行相应的错误处理(比如进入错误页面,显示错误组件之类),而这个函数本身是用来发送日志,不需要返回,也不需要await,所以直接fetch(也就是不用await),理论上能节省其它代码的处理时间
 */
export async function sendLog(
  message: string = '',
  level: string,
  context: string = '',
  data?: unknown
) {
  fetch(`${process.env.NEXT_PUBLIC_API_BASE_URL}/log`, {
    method: RequestMethods.post,
    body: JSON.stringify({
      message,
      level,
      context,
      sourceEnd: process.env.NEXT_PUBLIC_END,
      data,
    }),
  });
}

If I comment out export enum ..., my project will run well. But when I don't comment out export enum ..., it will show:

Build Error

Ecmascript file had an error

./src/lib/log.ts

Ecmascript file had an error
Server Actions must be async functions.

I think use server allows exporting types but not enum, which is crazy. It means I need to write my large number of enum in another file and import them?
I hope someone can help me answer my doubts or explain why it is designed in this way,thanks!

Additional information

No response

Example

No response

[maheshbhatiya73]

Hey! I totally get where you’re coming from — this behavior with export enum and server actions in Next.js can be really confusing at first.
What’s going on?
The core issue is about how Next.js Server Actions (those marked with 'use server') expect all exported functions to be async functions. This is because Server Actions run on the server and Next.js relies on their async nature to handle things like streaming, rendering, and routing correctly.

When you export an enum inside a file marked with 'use server', it’s not an async function, it’s a TypeScript construct that compiles into regular JavaScript code. This breaks Next.js’s expectation that all exports in a server actions file are async functions.

Why enums specifically?
enums are real runtime objects in JavaScript after compilation (unlike TypeScript types which vanish at runtime). So exporting them means you’re exporting something that is not async and doesn’t fit the server action contract.

What should you do?
Your intuition is right — the common pattern is to move your enums and other non-async exports into separate files that don’t have 'use server' at the top. Then import those enums into your server actions files as needed.

This way:

Your server actions file only exports async functions.

Enums live in a plain module, so no conflicts.

Your code stays clean and organized.

Why is it designed this way?
Next.js is still evolving its Server Actions API and has some strict rules currently to ensure consistent server/client boundaries and to optimize server rendering behavior. While it feels limiting, it helps prevent subtle bugs in production.

TL;DR
Server Actions files with 'use server' must export only async functions.

Exporting enums in the same file causes build errors because enums are not async functions.

Move enums to a separate file without 'use server' and import them.

This is expected behavior for now.
If you want, I can also help you with a quick example of how to organize the files. Just let me know!

[FatNerdPeng]

Thank you very much. Your answer has helped me understand the reason for this mistake, and I now know how to organize my project structure.