MERN Stack

What is the MERN stack?

MERN stands for MongoDB, Express, React, Node, after the four key technologies that make up the stack.

1. MongoDB — document database.

2. Express(.js) — Node.js web framework.

3. React(.js) — a client-side JavaScript framework.

4. Node(.js) — the premier JavaScript web server.

Express and Node make up the middle (application) tier. Express.js is a server-side web framework, and Node.js is the popular and powerful JavaScript server platform. Regardless of which variant you choose, ME(RVA)N is the ideal approach to working with JavaScript and JSON, all the way through.

React.js front end

The top tier of the MERN stack is React.js, the declarative JavaScript framework for creating dynamic client-side applications in HTML. React lets you build up complex interfaces through simple components, connect them to data on your back-end server, and render them as HTML.

React’s strong suit is handling stateful, data-driven interfaces with minimal code and minimal pain, and it has all the bells and whistles you’d expect from a modern web framework: great support for forms, error handling, events, lists, and more.

Express.js and Node.js server tier

The next level down is the Express.js server-side framework, running inside a Node.js server. Express.js bills itself as a “fast, unopinionated, minimalist web framework for Node.js,” and that is indeed exactly what it is. Express.js has powerful models for URL routing (matching an incoming URL with a server function), and handling HTTP requests and responses.

By making XML HTTP Requests (XHRs) or GETs or POSTs from your React.js front end, you can connect to Express.js functions that power your application. Those functions, in turn, use MongoDB’s Node.js drivers, either via callbacks or using promises, to access and update data in your MongoDB database.

MongoDB database tier

If your application stores any data (user profiles, content, comments, uploads, events, etc.), then you’re going to want a database that’s just as easy to work with as React, Express, and Node.

That’s where MongoDB comes in: JSON documents created in your React.js front end can be sent to the Express.js server, where they can be processed and (assuming they’re valid) stored directly in MongoDB for later retrieval.