mern-social | MERN stack based social media application [ Full-Stack | Runtime Evironment library

Writing routes directly can be confusing and difficult to manage if there are large number of routes. So according to MVC pattern, the application is divided into modules/logical blocks based on functionalities they perform. For example, a simple hospital management system can have authentication, billing, payroll , medical-stock , patients etc modules (imaginary). If you are building application using MVC pattern, the common practice is to write controller for each of the module. Express provides something called middleware also called as Router to attach these controllers to respective API routes (Imagine it as a sort of map that connects each route to respective controller).

Once you define routes for each of these modules through middleware, you use those routes with your application. These routes handle requests and send parameters to controller to process. You can learn how to use Middleware and Routers here : https://www.tutorialspoint.com/expressjs/expressjs_routing.htm

Regarding quality of code, dividing the code into modules and using routers to connect them is less tedious for others to understand. It also provides a good view of the application and it becomes easier to add new modules / functionality.

You can read more about building production-ready express app here : https://www.freecodecamp.org/news/how-to-write-a-production-ready-node-and-express-app-f214f0b17d8c/

Ad you said in the comments your Node.JS version is v6.10.0 unfortunately this version doesn't support async/await functions.

You can check Here: https://node.green/#ES2017-features-async-functions

Async/await support starts from version 7.0.0 where you need to add the --harmony flag to enable ES6/ES7 features. From 7.6.0 it is supported.

So, there are multiple ways you can achieve the same result.

1) Use Promise instead of async/await
2) Use babel to transpile the code into ES5. You can do this by running the code through babel-load if you are using webpack(mostly used for frontend products)
3) You can update your node to >7.6.x

Note: If you see in the package.json of that repository you can see that it is recommended to use node>8 for this project (accorind to the author)