Put simply, a middleware is a software layer situated between two or more pieces of software. This is an old concept in software development. Middleware is a term that has been in use since 1968. It gained popularity in the 1980s as a solution to the problem of how to link newer apps to older legacy systems. There are many definitions for it, such as (from Google Dictionary) "[middleware is a] software that acts as a bridge between an operating system or database and apps, especially on a network."
In the web development world, server-side software or apps, such as Koa and Express, take in a request and output a response. The middlewares are programs or functions that are executed in the middle after the incoming request, and they produce an output that could either be the final output or be used by the next middleware until the cycle is completed. This also means that we can have more than one middleware, and they will execute in the order...
