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fix(nextjs): support next.config.mts - #684
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Next.js supports next.config.mts, but the adapter threw an unsupported-extension error for it. .mts is always an ES module, so it is handled like .mjs: the renamed original is imported with its extension and the config is emitted as `export default`. Fixes #680
leoortizz
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Yuangwang,
abhis3 and
annajowang
as code owners
August 27, 2026 22:05
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This pull request adds support for the ".mts" (TypeScript ESM) file extension for Next.js configuration files. It updates the build process, config override logic, and restoration steps to recognize and correctly handle ".mts" files alongside existing formats like ".js", ".mjs", and ".ts". Additionally, a new unit test has been added to verify the override behavior for ".mts" configurations. I have no feedback to provide.
Yuangwang
approved these changes
Aug 31, 2026
This was referenced Sep 24, 2026
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Next.js supports next.config.mts, but the adapter threw an
unsupported-extension error for it.
.mts is always an ES module, so it is handled like .mjs:
the renamed original is imported with its extension and
the config is emitted as
export default.Fixes #680