Apple users
On desktop Safari, mobile Safari, and your native iOS app users can cast to a TV using AirPlay.
Google Chrome desktop users
On desktop users can cast to Google-compatible devices by visiting your web app in Google Chrome, clicking the three dots in the top right corner of the browser, clicking "Cast, Save, and Share", and then selecting their device.
Android users
Android users can cast to a Google-compatible device by installing the Google Home app and mirroring their mobile screen to their device.