A JavaScript developer designs, implements, and maintains websites and software applications using JavaScript programming language. They create interactive elements, improve user experience, and optimize web pages for maximum speed and scalability. They often work with frontend and backend technologies, integrating with APIs and data sources. In addition, they debug and troubleshoot code, maintain code quality, and collaborate with other team members. They also participate in code reviews, stay updated with latest industry trends, and often work with frameworks like React, Angular, or Vue.js. Furthermore, they ensure website functionality across different browsers and devices.