How do I detect if the app uses React Native, given APK file?

I can offer you 2 solutions:

• Solution 1

You can use dex2jar. When you open the generated jar file, you can check if it uses React Native if there is a folder /com/facebook/react/.

• Solution 2

  1. Rename your application APK app.apk into app.zip
  2. Decompress your zip file
  3. Use dexdump from AndroidSDK$ANDROID_HOME/build-tools//dexdump:dexdump classes.dex`
  4. Search for com/facebook/react in the output of dexdump

The accepted solution certainly will get you the right answer, but it will be quite slow. It is what I did originally, and it was not fast enough for my needs since I was running this script across hundreds of APKs. I developed an alternate solution and executed it before the original made it through 5% of the APKs.

The reason I don't like checking for layouts having com_facebook in the name (the other pre-existing solution) is that it is entirely plausible for an app to be using another Facebook SDK that contains a layout file starting with that string. I don't know of any false positives, but it seemed reasonably likely that there would be some.

Instead I check for the presence of libreactnativejni.so which I have to imagine only gets used if React Native is being used. (I originally was looking for libyoga.so, but I had a few false positives, I think because there's a logging library by the same name.)

Specifically, this condition on a Mac in a bash script is what I'm using (I think it's portable, but have not tested):

if [ "$(unzip -l $apkfile | grep libreactnativejni.so | wc -l)" -gt "0" ]
then 
echo "Uses RN"
fi