Suggestion: Add a flag to forbid use of global symbols

[shivanshu3]

The following code compiles in TypeScript but running the compiled output under Node.js results in an error:

> node foo.js
> ReferenceError: Person is not defined

Contents of foo.ts:

let a: Person = new Person();

Contents of bar.ts:

class Person {}

Contents of tsconfig.json:

{
	"compilerOptions": {
		"target": "es5",
		"module": "commonjs",
		"strict": true
	}
}

My understanding is that since bar.ts doesn't have any imports or exports, it is not a module, so the Person class becomes global. This behavior makes sense in a browser, but not in a Node.js application. There should be a compiler flag which forbids this behavior and produces a Cannot find name 'Person' error.

[mhegazy]

Duplicate of #18232

[shivanshu3]

Thank you very much for finding this issue @mhegazy !