A backend engineer specializing in Node.js, Express, MongoDB, MySQL, and JavaScript could be described as a "JavaScript Backend Engineer." Expertise in building efficient and scalable server-side applications using a variety of technologies, including Node.js, Express for routing and middleware, MongoDB for NoSQL databases, MySQL for relational databases, and JavaScript for programming the server-side logic. Capable of developing and integrating complex data models, implementing security measures, and optimising database performance to ensure seamless and secure application functionality.