What is MERN?

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1. Introduction

  • MERN stands for MongoDB, Express, React, and Node.

2. Big Picture for the MERN Architecture

  • Client (Browser):
    • ReactJS: Responsible for presentation and the user interface.
    • NodeJS & Express: Server-side responsible for business logic and file storage.
    • The server side and client side communicate with requests and responses in JSON format.
  • Database:
    • MongoDB: Responsible for persistent data storage.
    • NodeJS & Express communicate with MongoDB through database queries using the MongoDB SDK.

3. Diving into Client Side

  • React single-page application is served from the server to the browser.
  • React handles rendering everything in the browser.
  • React manages frontend or client-side routing with an extra library, react-router-dom.
  • react-router-dom helps render different React components based on the path the user enters into the URL bar of the browser.
  • The React application typically handles some front-end state that influences what is shown on the screen.
  • Developers build React components and style them.
  • React route configuration defines which React components are rendered for which path.
  • Implement state management with React hooks or Redux.

4. Understanding the Server Side

  • Decoupled Ends:
    • Frontend powered by React.
    • Backend powered by Node Express.
    • Database server powered by MongoDB.
  • Backend:
    • Built as an API (Application Programming Interface).
    • Uses a REST API (Representational State Transfer).
    • APIs perform various actions on the server, such as storing data in a database, validating user input, and retrieving data from a database.
    • REST API uses a combination of different URLs and HTTP verbs (GET, POST, PATCH, DELETE) to build endpoints that trigger different actions when a client makes a request.
    • The REST API executes code on the server.
    • The Node Express server communicates with the database.

5. More About REST

  • Client-Server Combination:
    • The server uses Node Express, which communicates with MongoDB, and the client uses React.
    • A request is a combination of a specific URL, for example, www.yourpage.com/user.
    • The URL combined with a specific HTTP verb triggers a specific action.

REST & HTTP Methods (HTTP Verbs)

  • GET: Retrieve a resource from the server.
  • POST: Create or append a resource on the server.
  • PUT: Create or overwrite a resource on the server.
  • PATCH: Update parts of an existing resource on the server.
  • DELETE: Delete a resource on the server.
  • OPTIONS: Determine whether follow-up requests are allowed (sent automatically).

6. Connecting Node & React

6.1 One Server Hosts Node API & React SPA

  • One server hosts both the Node API and the React single-page application under the same domain.
  • For example, mypage.com/ might return the single-page application, while mypage.com/api serves the endpoints for the React single-page application to communicate with.
  • The Node Express API handles incoming requests on the server. Requests targeting mypage.com/api reach the API, and other requests return the React single-page application.
  • Data is exchanged between the React app and the Node API in JSON format.

6.2 Two Separate Servers

  • One server serves the single React.js application HTML page.
  • Another server hosts the Node (Express) API, which handles incoming requests.
  • Data is exchanged between the React app and the Node API in JSON format.

6.3 MongoDB Database

  • MongoDB always has its own database server. This server could be installed on the same physical machine as the Node and React app.

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