Afaik TypeScript is using https://www.npmjs.com/package/reflect-metadata https://www.npmjs.com/package/reflect-metadata to attach runtime type information, some

Afaik TypeScript is using https://www.npmjs.com/package/reflect-metadata https://www.npmjs.com/package/reflect-metadata to attach runtime type information, something angular asked them to do (there was no runtime information before). See also: https://github.com/Microsoft/TypeScript/issues/3148 https://github.com/Microsoft/TypeScript/issues/3148