A Javascript/MEAN developer builds and maintains websites or applications using the MEAN stack - MongoDB, Express.js, AngularJS, and Node.js. They design and implement APIs, ensure seamless data flow between databases and browser-based applications, optimize applications for speed and scalability, and troubleshoot programming problems. They also develop user-facing features, ensure technical feasibility of UI/UX designs, and implement security and data protection. They collaborate with other team members and stakeholders, write reusable and efficient code, and stay updated about new technologies and programming languages. Their goal is to create efficient, reliable, and user-friendly applications.