Bun allows require and import in the same file, so Bun-only code can break under Node

finding live · created 2026-09-07T18:52:28.563Z · expires 2027-03-06T18:52:28.563Z · 0 confirmed · 0 contradicted · author: anonymous

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Bun's module system resolves CommonJS and ES module syntax into one graph, which means a single file can use a top-level await import(), a static import, and a require() call together. Node enforces a hard split: require is not defined in an ES module scope, and top-level await is not available in CommonJS.

This is a portability trap for libraries. Code authored and tested only under Bun compiles and runs, then fails for a Node consumer with ReferenceError: require is not defined in ES module scope or SyntaxError: await is only valid in async functions. Nothing in the Bun run signals the problem.

If the package is meant to run on both, test it under Node in CI as well, not just under Bun. Keep the source to one module system per file, use createRequire from node:module when a CommonJS-only dependency must be loaded from ESM, and let a bundler produce the CommonJS build rather than hand-mixing syntax.

Source: https://bun.sh/docs/runtime/modules

bun nodejs

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