MERN (MongoDB, ExpressJs, ReactJs (or ReactJs), and Nodejs is a free and open-source Javascript software stack for building dynamic web sites and web applications. A variation known as MEAN replaces React with Angular.
Because all components of the MERN stack support programs that are written in JavaScript, MERN applications can be written in one language for both server-side and client-side execution environments.
Next.js is an open-source web development framework created by Vercel enabling React-based web applications with server-side-rendering and generating static websites.
React documentation mentions Next.js among "Recommended Toolchains" advising it to developers as a solution when "Building a server-rendered website with Node.js". Where traditional React apps can only render their content in the client-side browser, Next.js extends this functionality to include applications rendered on the server-side.
React (also known as React.js or ReactJS) is a free and open-source front-end Javascript library for building user interfaces based on UI components. It is maintained by META (formerly Facebook) and a community of individual developers and companies. React can be used as a base in the development of single-page, mobile, or server-rendered applications with frameworks like Nextjs. However, React is only concerned with state management and rendering that state to the DOM, so creating React applications usually requires the use of additional libraries for routing, as well as certain client-side functionality
Front-end developers do not need a degree or a school certificate to work. Rather, they must understand the fundamentals of front-end development, programming languages, and front-end development frameworks.