A Cylon.js developer works on robotics and Internet of Things (IoT) applications using the Cylon.js JavaScript framework. They design, develop, test, and debug software that enables devices to communicate with each other seamlessly. Their responsibilities include creating code for robot's sensors and actuators, integrating various hardware devices, and ensuring interoperability of systems. They also work on improving system performance and resolving technical issues. Additionally, they work on the security aspect of IoT devices and collaborate with other team members to create end-to-end IoT solutions. They need strong problem-solving skills and a deep understanding of JavaScript and robotics.