A Full Stack JavaScript (JS) Developer is a professional who has expertise in both front-end and back-end web development using JavaScript as the primary programming language. This role involves working with various technologies and frameworks to build web applications that include user interfaces and server-side functionality. Here’s what you should know about being a Full Stack JS Developer:

1. Front-End Development:
   1. Full Stack JS Developers are skilled in front-end development, which includes creating the user interface and user experience of web applications.
   2. They use HTML, CSS, and JavaScript to build responsive and interactive web pages.
   3. Knowledge of front-end libraries and frameworks like React, Angular, or Vue.js is often required.
2. Back-End Development:
   1. Full Stack JS Developers are proficient in server-side programming using JavaScript.
   2. They work with back-end technologies like Node.js, Express.js, and other Node.js frameworks to handle server logic, database operations, and API development.
   3. Knowledge of databases (SQL and NoSQL) and how to interact with them is essential.
3. Full-Stack Proficiency:
   1. These developers bridge the gap between front-end and back-end development, allowing them to work on all aspects of a web application.
   2. They design and implement RESTful APIs, handle authentication and user sessions, and manage data storage.