A datatable.js developer is responsible for designing, implementing and maintaining dynamic and interactive tables on web applications using the DataTables JavaScript library. They write clean, scalable code to ensure the functionality of these tables, which can include sorting, searching and pagination features. They troubleshoot and fix bugs, improve user experience, and optimize performance. Additionally, they may integrate DataTables with other technologies like AJAX, JSON, or server-side languages to manage data. They also ensure cross-browser compatibility and responsiveness. Their role may also involve collaborating with other team members and participating in the software development lifecycle.