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Improve Proxy invalid export error message by devjiwonchoi · Pull Request #84887 · vercel/next.js · GitHub
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@devjiwonchoi devjiwonchoi commented Oct 15, 2025

Improve invalid Proxy/Middleware export error message to:

> Build error occurred
Error: The file "./proxy.ts" must export a function, either as a default export or as a named "proxy" export.
This function is what Next.js runs for every request handled by this proxy (previously called middleware).

Why this happens:
- You are migrating from `middleware` to `proxy`, but haven't updated the exported function.
- The file exists but doesn't export a function.
- The export is not a function (e.g., an object or constant).
- There's a syntax error preventing the export from being recognized.

To fix it:
- Ensure this file has either a default or "proxy" function export.

Learn more: https://nextjs.org/docs/messages/middleware-to-proxy

Turbopack:

Error: Turbopack build failed with 1 errors:
./proxy.ts
Proxy is missing expected function export name
This function is what Next.js runs for every request handled by this proxy (previously called middleware).

Why this happens:
- You are migrating from `middleware` to `proxy`, but haven't updated the exported function.
- The file exists but doesn't export a function.
- The export is not a function (e.g., an object or constant).
- There's a syntax error preventing the export from being recognized.

To fix it:
- Ensure this file has either a default or "proxy" function export.

Learn more: https://nextjs.org/docs/messages/middleware-to-proxy

Closes NEXT-4741

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devjiwonchoi commented Oct 15, 2025

@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 7850088 to cc9f03b Compare October 15, 2025 03:06
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy branch from 68b0225 to a796ac4 Compare October 15, 2025 03:08
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from cc9f03b to 54887d7 Compare October 15, 2025 03:08
@devjiwonchoi devjiwonchoi changed the base branch from jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy to graphite-base/84887 October 15, 2025 12:57
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 54887d7 to 1b140cd Compare October 15, 2025 12:58
@devjiwonchoi devjiwonchoi changed the base branch from graphite-base/84887 to jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy October 15, 2025 12:58
@devjiwonchoi devjiwonchoi requested review from feedthejim and icyJoseph and removed request for feedthejim and icyJoseph October 15, 2025 12:59
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 1b140cd to 89d1fac Compare October 15, 2025 14:06
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy branch from c132d3e to 638c730 Compare October 15, 2025 14:06
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 89d1fac to d5a7788 Compare October 15, 2025 17:51
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy branch from 638c730 to 3a0a169 Compare October 15, 2025 17:51
@devjiwonchoi devjiwonchoi changed the base branch from jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy to graphite-base/84887 October 15, 2025 18:30
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from d5a7788 to 999ed9e Compare October 16, 2025 15:57
@devjiwonchoi devjiwonchoi changed the base branch from graphite-base/84887 to jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy October 16, 2025 15:57
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 999ed9e to 38d426a Compare October 16, 2025 16:23
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy branch from 585ff17 to 172162a Compare October 16, 2025 16:23
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 38d426a to 3f4b756 Compare October 16, 2025 16:32
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-fix_throw_error_during_build_when_invalid_export_for_proxy branch from 172162a to f19dbfb Compare October 16, 2025 16:32
@mischnic mischnic force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch 2 times, most recently from 926983c to ccc6110 Compare October 20, 2025 23:13
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch 2 times, most recently from c88daf8 to a85a3e9 Compare October 21, 2025 05:35
@mischnic mischnic force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from a85a3e9 to 2918422 Compare October 21, 2025 05:38
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 2918422 to 5e00469 Compare October 21, 2025 05:49
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from 0c6f0f4 to dfa6498 Compare October 21, 2025 16:55
@devjiwonchoi devjiwonchoi force-pushed the jiwon/10-15-improve_proxy_invalid_export_error_message branch from c0da357 to b293ddd Compare October 21, 2025 18:20
@devjiwonchoi devjiwonchoi merged commit 409b281 into canary Oct 21, 2025
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@devjiwonchoi devjiwonchoi deleted the jiwon/10-15-improve_proxy_invalid_export_error_message branch October 21, 2025 20:55
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