Consider the following code snippet below

(async () => {
    const app = express();
    let test = "test string";

    app.get('/numbers', (req, res) => {
        res.send(test);
    }

    app.listen( 8000, () => {
      console.log( `server running http://localhost:8000`);
    });
)();

If I run the above code snippet, the server starts listening on localhost:8000.

How is that working?
How am I able to access test variable in my get method? Wouldn't the test variable be destroyed once the topmost function has finished executing?