  We introduce SmartControllerJS, a new JavaScript library for fast,
cost-effective designing of web applications controlled via everyday
smartphones. At its core, SmartControllerJS establishes a connection between
two webpages, one page running on a desktop browser and the other on the user's
smartphone. The smartphone webpage loads a controller interface allowing users
to control a web application running on their computer's browser. The
SmartControllerJS framework enables fast iteration loops when designing
interactive user experiments because it has minimal friction and allows for
scaling, while having no running costs. We first describe how this library is
built, how it can be used, and provide interactive examples. We then present
two games designed for public screens along with results from user studies
evaluating acceptability and ease of use. Finally, we implement a custom
controller based on user feedback and introduce connection monitoring tools. We
believe SmartControllerJS can accelerate the design of interactive experiments
for researchers in Human-Computer Interaction, and be a useful tool for
educational projects. All our code is available at
https://github.com/SmartControllerJS and links to all demos can be found in
Table I. To explore our demos, we recommend reading this work on a desktop
computer with your smartphone in hand.
