Using a Simulator / Emulator
There is no substitute to testing the performance and feel of your app on an actual device, but when it comes to debugging you might have an easier time using an emulator/simulator.
Apple refers to their emulator as a “Simulator” and Google refers to theirs as an “Emulator”.
Make sure you have the latest Xcode (e.g. from the Mac App Store). This includes the iOS Simulator, among several other tools.
On Android we recommend the Genymotion emulator over the standard emulator — we have found it to be more feature complete, faster and easier to use.
Download Genymotion (free version) and follow the Genymotion installation guide. Once you’ve installed Genymotion, create a virtual device - we recommend a Nexus 5, the Android version is up to you. Start up the virtual device when it’s ready. If you run into any issues follow our Genymotion guide.
This menu gives you access to several functions which are useful for debugging. It is also known as the Debug Menu. Invoking it depends on the device where you are running your application.
On an iOS Device
Shake the device a little bit.
On iOS Simulator
Ctrl-Cmd-Z on a Mac in the emulator to simulate the shake gesture, or press
Either press “Menu” button in Genymotion’s toolbar, or just hit
To ensure the best debugging experience, first change your host type in XDE to
localhost. If you use
Tunnelwith debugging enabled, you are likely to experience so much latency that your app is unusable. While here, also ensure that
Development Modeis checked.
If you are using
LAN, make sure your device is on the same wifi network as your development machine. This may not work on some public networks.
localhostwill not work for iOS unless you are in the simulator, and it only work on Android if your device is connected to your machine via usb.
Line numbers for
console.logstatements don’t work by default when using Chrome debugging. To get correct line numbers open up the Chrome Dev Tools settings, go to the “Blackboxing” tab, make sure that “Blackbox content scripts” is checked, and add
expo/src/Logs.jsas a pattern with “Blackbox” selected.
Troubleshooting localhost debugging
When you open a project in XDE and when you press
Open on Android, XDE will automatically tell your device to forward
19001 to your development machine, as long as your device is plugged in or emulator is running. If you are using
localhost for debugging and it isn’t working, close the app and open it up again using
Open on Android. Alternatively, you can manually forward the ports using the following command if you have the Android developer tools installed:
adb reverse tcp:19000 tcp:19000 -
adb reverse tcp:19001 tcp:19001
Source maps and async functions
Source maps and async functions aren’t 100% reliable. React Native doesn’t play well with Chrome’s source mapping in every case, so if you want to make sure you’re breakpointing in the correct place, you should use the
debugger call directly from your code.
To debug your app’s HTTP requests you should use a proxy. The following options will all work:
On Android, the Proxy Settings app is helpful for switch between debug and non-debug mode. Unfortunately it doesn’t work with Android M yet.
There is future work to get network requests showing up in Chrome DevTools.
Hot Reloading and Live Reloading
Hot Module Reloading is a quick way to reload changes without losing your state in the screen or navigation stack. To enable, invoke the developer menu and tap the “Enable Hot Reloading” item. Whereas Live Reload will reload the entire JS context, Hot Module Reloading will make your debug cycles even faster. However, make sure you don’t have both options turned on, as that is unsupported behavior.
Other Debugging Tips
Dotan Nahum outlined in his “Debugging React Native Applications” Medium post other useful tools such as spying on bridge messages and JSEventLoopWatchdog.
Still have questions? Ask on our forums!