Middleware is software glue

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Middleware is computer software that provides services to software applications beyond those available from the operating system. It can be described as software glue.

 Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. These functions are used to modify req and res objects for tasks like parsing request bodies, adding response headers, etc.
  • functions that have access to the request and response
  • gets called before the controller function
  • can modify the request object that gets passed to the controller
  • can send a response and prevent the controller being accessed
  • used for common tasks that are not the responsibility of any single
  • controller:
    • authentication
    • request Body Validation
    • logging
    • redirection
    • error handling
  • can be applied at application or route level
    • application level applies to all requests
    • route level applies to certain routes
  • express comes with a few builds in middleware functions
    • express.json - parses JSON requests
    • express.static - serves static files
  • can also install others from npm, or write your own

Middleware: THE core of node.js backend apps - https://hackernoon.com/middleware-the-core-of-node-js-apps-ab01fee39200
Express.js Middleware Demystified - https://www.safaribooksonline.com/blog/2014/03/10/express-js-middleware-demystified/
Using middleware - https://expressjs.com/en/guide/using-middleware.html

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