How to do logging in React Native?

console.log works.

By default on iOS, it logs to the debug pane inside Xcode.

From the iOS simulator, press (⌘+D) and press Remote JS Debugging. This will open a resource, http://localhost:8081/debugger-ui on localhost. From there, use the Chrome Developer tools JavaScript console to view console.log

Pre React Native 0.29, run this in the console:

adb logcat *:S ReactNative:V ReactNativeJS:V

Post React Native 0.29, run:

react-native log-ios

or

react-native log-android

As Martin said in another answer.

This shows all console.log(), errors, notes, etc. and causes zero slow down.

Use console.log, console.warn, etc.

As of React Native 0.29, you can simply run the following to see logs in the console:

react-native log-ios
react-native log-android