Next.js 16 "use server" Export Compliance

Problem

Next.js 16 enforces strict rules for files with the "use server" directive: they can only export async functions. Any attempt to export constants, objects, enums, or type definitions from these files will cause a build error:

Error: A "use server" file can only export async functions, found object.
Read more: https://nextjs.org/docs/messages/invalid-use-server-value

This error is not immediately obvious because:

The error message doesn't clearly indicate which export is problematic
Many developers expect to co-locate related constants with their server actions
TypeScript compilation succeeds but Next.js build fails

Context / Trigger Conditions

When to use this skill:

Exact error message: Build fails with A "use server" file can only export async functions, found object
File structure: You have a file with "use server" at the top that exports both:
- Async server actions (functions)
- Constants, objects, enums, or types
Common scenarios:
- Exporting audit action constants (e.g., AUDIT_ACTIONS)
- Exporting Zod validation schemas alongside server actions
- Exporting TypeScript enums or type definitions
- Exporting configuration objects

Example problematic file:

"use server";

// ❌ This causes the error
export const AUDIT_ACTIONS = {
  USER_CREATED: "USER_CREATED",
  USER_UPDATED: "USER_UPDATED",
} as const;

// ✅ This is allowed
export async function createUser() {
  // ... server action logic
}

Solution

Step 1: Create a new constants file (without "use server")

Create a separate file for your non-function exports. Do NOT add "use server" to this file.

// lib/constants/audit-actions.ts  (NO "use server" directive)

/**
 * Audit log action types for user management
 */
export const AUDIT_ACTIONS = {
  USER_CREATED: "USER_CREATED",
  USER_UPDATED: "USER_UPDATED",
  USER_DELETED: "USER_DELETED",
} as const;

export type AuditAction = (typeof AUDIT_ACTIONS)[keyof typeof AUDIT_ACTIONS];

Step 2: Keep only async functions in your server actions file

// lib/actions/user.ts
"use server";

import { AUDIT_ACTIONS, type AuditAction } from "@/lib/constants/audit-actions";
import { createAuditLog } from "@/lib/utils/audit-log";

export async function createUser(data: unknown): Promise<ActionResult> {
  // ... implementation using AUDIT_ACTIONS.USER_CREATED
}

export async function updateUser(data: unknown): Promise<ActionResult> {
  // ... implementation using AUDIT_ACTIONS.USER_UPDATED
}

Step 3: Update imports in other files

Update any files that imported the constants from the server actions file:

// Before
import { AUDIT_ACTIONS } from "@/lib/actions/user";

// After
import { AUDIT_ACTIONS } from "@/lib/constants/audit-actions";

Step 4: Update test mocks

If you have unit tests that mock the constants, update the mock paths:

// tests/unit/actions/user.test.ts

vi.mock("@/lib/constants/audit-actions", () => ({
  AUDIT_ACTIONS: {
    USER_CREATED: "USER_CREATED",
    USER_UPDATED: "USER_UPDATED",
  },
}));

Verification

After applying the fix:

TypeScript check: Run turbo types or tsc --noEmit - should pass
Build: Run turbo build or next build - should complete without errors
Runtime: Server actions should work exactly as before
Tests: Unit tests should pass with updated import paths

Success indicators:

✅ No "use server" export errors in build output
✅ All async server action functions still exported correctly
✅ Constants accessible via new import path
✅ TypeScript types properly inferred

Example: Real-World Case

Before (causes error):

// lib/utils/audit-log.ts
"use server";

export const AUDIT_ACTIONS = {
  LANGUAGE_CHANGED: "LANGUAGE_CHANGED",
  TIMEZONE_CHANGED: "TIMEZONE_CHANGED",
  ACCESSIBILITY_CHANGED: "ACCESSIBILITY_CHANGED",
} as const;

export type AuditAction = (typeof AUDIT_ACTIONS)[keyof typeof AUDIT_ACTIONS];

export async function createAuditLog(params: { action: AuditAction }): Promise<void> {
  // ... implementation
}

After (works correctly):

// lib/constants/audit-actions.ts (NEW FILE - no "use server")
export const AUDIT_ACTIONS = {
  LANGUAGE_CHANGED: "LANGUAGE_CHANGED",
  TIMEZONE_CHANGED: "TIMEZONE_CHANGED",
  ACCESSIBILITY_CHANGED: "ACCESSIBILITY_CHANGED",
} as const;

export type AuditAction = (typeof AUDIT_ACTIONS)[keyof typeof AUDIT_ACTIONS];

// lib/utils/audit-log.ts
"use server";

import type { AuditAction } from "@/lib/constants/audit-actions";

export async function createAuditLog(params: { action: AuditAction }): Promise<void> {
  // ... implementation
}

export async function getRequestMetadata(): Promise<{ ipAddress: string; userAgent: string }> {
  // ... implementation
}

// lib/actions/preferences.ts
"use server";

import { AUDIT_ACTIONS } from "@/lib/constants/audit-actions";
import { createAuditLog } from "@/lib/utils/audit-log";

export async function updateLanguage(data: unknown): Promise<ActionResult> {
  // ... implementation
  await createAuditLog({
    userId: user.id,
    action: AUDIT_ACTIONS.LANGUAGE_CHANGED, // ✅ Works perfectly
  });
}

Notes

Why This Restriction Exists:

Server Actions in Next.js 16 rely on the async nature of exported functions for streaming, rendering, and routing
The framework needs to track and serialize server functions differently from regular exports
Mixing function and non-function exports makes the bundling and serialization process ambiguous

Common Mistakes:

❌ Adding "use server" to the new constants file (defeats the purpose)
❌ Using default exports for constants (makes refactoring harder)
❌ Forgetting to update test mocks after moving constants
❌ Trying to export utility functions that aren't async (these also need to be async or moved)

Related Patterns:

This same pattern applies to Zod schemas, configuration objects, and TypeScript enums
You can co-locate related constants by using a constants/ directory structure
Consider using barrel exports (index.ts) to simplify imports from multiple constant files

Next.js 16 Async Requirements:

All "use server" exports must be async functions
Utility functions in server action files must also be async (even if they don't await anything)
Helper functions like error(), success(), validateInput() should be async and awaited

nextjs-16-use-server-exports