NOTE: My expo-web repo has been merged in official Expo, Yay!
NOTE2: Unfortunately the PR had to be retracted due to dependency concerns.
Also I'm now doubting if this is the correct way to move forward. It seems Vincent Riemers React Native DOM is the better way to go than react-native-web.
I will soon update this repo to use that instead. (update: not going to happen)
This repo shows how an Expo app (the default tabs template) can be extended with React Native Web support.
Clone this repo, and run yarn.
Then start exp start -c in one terminal, in another start exp ios.
In yet another terminal start yarn start and connect your browser to http://localhost:8080.
Try resizing the browser.