How to Change Expo React Native Default Port 19000

In your package.json file change

"start": "expo start"

to

"start": "expo start --port 19001"

npx expo start --port=<YOUR_PORT>

You can set the RCT_METRO_PORT environment variable (for Metro) and/or WEB_PORT (for Webpack), e.g.:

RCT_METRO_PORT=11111 WEB_PORT=22222 expo start

These seem to be undocumented, however, so use with care.

I spent hours with reading source codes but unable to find the config. I ended up updating startDevServerAsync.js script with the port I wanted. (I admit this is not good but I can't spend more time on just dealing with this)

$ which expo-cli
/home/shohey1226/.nvm/versions/node/v14.15.5/bin/expo-cli
$ cd  ~/.nvm/versions/node/v14.15.5/lib/node_modules/expo-cli/node_modules/xdl/build/start
$ sed -i 's/19000/8080/g' startDevServerAsync.js

To change the default port, you can create an .exprc file in your project root with

{
  "manifestPort": valid port number (e.g. 19002)
}

You can specify this using the following CLI command:

npx react-native start --port=<YOUR_PORT>

as documented here.