ts-node not giving error when using named import from a module which has some error

[aswinsvijay]

I was using ts-node to test a server, when I came across a specific issue. A minimal reproduction of the problem is shown.

// main.ts

import { FunctionInterface } from "./module";

const Implementation: FunctionInterface = (name, age) => {};

console.log(Implementation);

// module.ts

export interface FunctionInterface {
  (name: string, age: number): ValueInterface;
}

Now in module.ts ValueInterface was never defined (or maybe was defined somewhere else but not imported), but ts-node does not give the expected "cannot find name" error.
Is there a way to fix this?

[agammann]

I reproduced this with ts-node 10.9.2 and TypeScript 5.9.3: running main.ts did not report the missing name inside module.ts, but a project type check did:

npx tsc --noEmit --project tsconfig.json

That reports TS2304: Cannot find name 'ValueInterface' in module.ts. Use this as a separate development/CI check alongside ts-node; executing an entry point is not a complete project diagnostic pass. In your example, FunctionInterface is only used as a type, so its import is also removed from the JavaScript that runs.

Define/export ValueInterface or import it where the interface is declared. After giving it a concrete object type, ts-node also rejected the implementation's empty body: (name, age) => {} returns void, whereas the interface requires ValueInterface. You will need to return a value of that type too.

If you use transpileOnly or SWC, those modes skip TypeScript checking altogether; the separate tsc --noEmit check is especially useful there. ts-node's performance documentation discusses separating type checking from execution.