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.
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.
Shake the device a little bit.
Ctrl-Cmd-Z on a Mac in the emulator to simulate the shake gesture, or press
Cmd+M, or run
adb shell input keyevent 82 in your terminal window.
To ensure the best debugging experience, first change your host type in Expo Dev Tools to
localhost. If you use
Tunnel with debugging enabled, you are likely to experience so much latency that your app is unusable. While here, also ensure that
Development Mode is 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.
localhost will 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.
Open the app on your device, reveal the developer menu then tap on
Debug JS Remotely. This should open up a Chrome tab with the URL
Line numbers for
console.log statements 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.js as a pattern with "Blackbox" selected.
When you start a project with Expo CLI and when you press
Run on Android device/emulator in Expo Dev Tools (or
a in the terminal), Expo CLI 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 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 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.