async function start({ app, router }) {
  app.use(router);

  app.mount('#q-app');
}
THIS FILE IS GENERATED AUTOMATICALLY.
DO NOT EDIT.

You are probably looking on adding startup/initialization code.
Use "quasar new boot <name>" and add it there.
One boot file per concern. Then reference the file(s) in quasar.config.js > boot:
boot: ['file', ...] // do not add ".js" extension to it.

Boot files are your "main.js"