• Code that sits between different parts of an application
• A simple mental model that is a pipe

# Express

• middleware functions with access to req and res objects
• execute code to make changes to the req and res objects
• end the req/res cycle
• or call the next middleware function
• types
  • application level
  • router level
  • error handling
  • built-in
    • express.static
    • express.json
    • exprses.urlencoded
  • 3rd party

# References

https://stackoverflow.com/questions/2904854/what-is-middleware-exactly https://expressjs.com/en/guide/using-middleware.html