next.config.ts does not support top-level-await

[stefanprobst]

Link to the code that reproduces this issue

https://github.com/stefanprobst/issue-next.config.ts-await

To Reproduce

• clone https://github.com/stefanprobst/issue-next.config.ts-await
• pnpm install && pnpm run dev
• see error message:

ReferenceError: await is not defined

Current vs. Expected behavior

top-level await works in next.config.js but not in next.config.ts.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #41~22.04.2-Ubuntu SMP PREEMPT_DYNAMIC Mon Jun  3 11:32:55 UTC 2
  Available memory (MB): 15893
  Available CPU cores: 4
Binaries:
  Node: 20.14.0
  npm: 10.7.0
  Yarn: N/A
  pnpm: 9.5.0
Relevant Packages:
  next: 15.0.0-canary.67 // Latest available version is detected (15.0.0-canary.67).
  eslint-config-next: N/A
  react: 19.0.0-rc.0
  react-dom: 19.0.0-rc.0
  typescript: 5.5.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

TypeScript

Which stage(s) are affected? (Select all that apply)

next dev (local)

Additional context

No response

[devjiwonchoi]

Thank you for reporting this! We will surely get this fixed before going stable. Thank you once again!

[karlhorky]

For anyone looking for a workaround for ESM / top-level await support until PR #68365 lands, I added a workaround with a node_modules patch here:

• fix(next-config-ts): properly handle ESM #68365 (comment)

[stefanprobst]

@karlhorky does https://nextjs.org/docs/app/api-reference/next-config-js#async-configuration work as a workaround for your usecase?

[karlhorky]

My use case (documented in my comments in #68365) is actually not even top-level await - it was an ESM-only library failing with ERR_PACKAGE_PATH_NOT_EXPORTED when imported in next.config.ts 😮