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Backend question · TypeScript › TypeScript on the server

The tsconfig uses "module": "NodeNext" and package.json has "type": "module". What happens with this import in src/app.ts?

import { db } from "./db";   // the file is src/db.ts
Compile error: relative ESM imports need an explicit extension, so write ./db.js

It is a compile error, and you must write ./db.js. Node's ESM loader does not guess file extensions. tsc does not add them either. So TypeScript requires the extension that the emitted file will have. You write ./db.js, and TypeScript maps it to db.ts for type checking.

"tsc adds .js to the specifier in the output" is wrong, because tsc never rewrites import paths here. "Node resolves ./db to ./db.js at runtime" is wrong, because Node's ESM loader does not guess extensions. "you must write ./db.ts" is wrong, because the import must name the emitted .js file.