Typescript doesn't complain about missing imports

Question

Contents of foo.ts:

let a: Person = new Person();

Contents of bar.ts:

class Person {}

The tsconfig.json file contains the default set of values created by tsc --init.

I'm using typescript version 2.6.2.

The code above simply compiles with no errors about Person being not defined. If I rename Person to Persons in foo.ts, then it does throw an error saying cannot find name 'Persons'. So it's as if it is automatically importing this file somehow.

Also note that I'm not exporting the Person class in bar.ts. If I do add an export statement, then everything behaves as it should - I get an error saying cannot find name 'Person'.

Does anyone know what's going on here? Is this a user error?

Edit:

Maybe this makes sense in the browser, but to me this behavior makes no sense in a node.js application. Is there a Typescript flag which forbids this behavior?

Answer 1

Your bar.ts is not a module, since it doesn't have any import nor any export. So it defines a global Person class, that doesn't need to be imported, since it's global. Export it, and TypeScript will complain about the missing import.