Exponent Apps - testing on Multiple Form factors

Want to test your exponent app on multiple screen sizes ? Check out maya-kai
Exponent is a great way to build mobile apps - you get all the benefits of React Native, with none of the pain of installing the Android SDK or XCode. Since Exponent is now integrated into VSCode, my developer workflow pretty much involves firing up the VSCode editor and debugging the app running on exponent in my devices.
Despite an efficient authoring workflow, testing my app across devices is still a little cumbersome. With the need to support different devices and screen sizes, I still have to perform the typical test scenarios manually over all the devices.

User gesture mirroring for React Native

Last year, I had blogged about a project that lets you mirror user gestures across devices for React Native apps. This has the same functionality that browsersync has for websites. This library lets you interact with just one device and as the test scenario progresses, you can view the user controls across other devices with different screen sizes. Though this library was for originally meant for React Native, the code is all JavaScript and uses React's Event Model. This blog post explores the idea of trying out the library with apps on Exponent.

Exponent + Maya-kai

Surprisingly, no changes were required to make it work with Exponent! I simply npm install maya-kai --save and import it in main.js using var mk=require('maya-kai'); mk.start(); The devices (2 phones, 1 iPad) were on the LAN, so I just needed to ensure that the maya-kai server was accessible to them.

To automate this even more, I added a task that also launches my app on all the connected Android devices when I start the tests.

adb devices | egrep '\t(device|emulator)' | cut -f 1 | xargs -t -J% -n1 -P5 adb -s % shell am start -a android.intent.action.VIEW -d exp://<exponent URL>

I was unable to find an equivalent for iOS though.

Other developer workflow actions like live reload and hot module replacement also worked on all devices. General developer is also faster since there is no native app "install" process here.

Wishlist for Exponent 

  • If user gesture mirroring is be something built into Exponent, additional setup steps would not be needed anymore.
  • It would also be good to automate the process of launching the app for iOS devices when starting tests.  
  • There is also no dev vs production mode, so I am currently using 2 different apps, one for testing, and the other one being the real, published app, without Maya-kai embedded.


I think that this workflow is great for quickly testing multiple form factors. I could simply publish my exponent app, launch it on multiple devices and interact with them. This is also a neat way to share screen with remote clients - simply enable gesture mirroring and you can walk someone through you app's workflow.
I am also looking at integrating this with Appetize, enabling a virtual device wall, something that I did for Cordova applications.