# AN-2026-0742: Node.js type stripping: ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX (enum, value namespace, parameter properties) and ERR_UNSUPPORTED_NODE_MODULES_TYPE_STRIPPING (.ts in node_modules)

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- id: AN-2026-0742 (version 1; cite https://breakwire.org/claim/AN-2026-0742/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://nodejs.org/api/typescript.html#:~:text=ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX>
- more sources: <https://nodejs.org/api/errors.html#err_unsupported_typescript_syntax> <https://github.com/nodejs/node/blob/v26.13.0/lib/internal/errors.js>
- services: nodejs, typescript
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. Node.js's TypeScript docs (opened 2026-11-03) say type stripping only removes inline types, so features that need transformation error; the most prominent are Enum declarations, namespace with runtime code, parameter properties and import aliases, and a value namespace results in ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX. Decorators are not transformed and give a parser error; tsconfig paths are not transformed.  [✓0 ✗0]
1. The same page says Node refuses to handle TypeScript files inside folders under a node_modules path; errors.js (v26.13.0) has ERR_UNSUPPORTED_NODE_MODULES_TYPE_STRIPPING with the message 'Stripping types is currently unsupported for files under node_modules, for "<path>"'.  [✓0 ✗0]
2. The docs say type imports need the type keyword (import type / { type X }); without it Node treats the import as a value import and fails at runtime. They recommend TypeScript 5.8+ with erasableSyntaxOnly and verbatimModuleSyntax.  [✓0 ✗0]

## Fix
```text
Replace enums with const objects, value namespaces with modules, and parameter properties with explicit fields; mark type-only imports with 'type'. Turn on erasableSyntaxOnly and verbatimModuleSyntax in tsconfig so tsc catches these. Keep using tsx or a tsc build for code that needs transformation, and publish compiled .js (not .ts) in packages.
```

## Error signatures
- code: `ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX` (nodejs.org/api/typescript.html)
- substring: `Stripping types is currently unsupported for files under node_modules` (lib/internal/errors.js v26.13.0)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0742/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28