Download this repo and run a static web server to host this app. (Note that you don't need to use our web server; you can use any web server you want, as long as content is hosted at http://localhost:8000/fhir-app).
git clone https://github.com/jmandel/argonaut-sprint-2-example-client
cd argonaut-sprint-2-example-client
npm install
npm run serve
Then launch a local browser and open http://localhost:8000/fhir-app/launch.html.
You should be directed to approve access, and upon successful completion you'll see a JSON patient bundle response in your browser.