Middleware in Express

• Look at https://github.com/kurmasz-SampleCode/CIS371-SampleCode/tree/master/ExpressRouting
• First few examples (books, toys) just demonstrate that the first route to match is run, so choose route orders carefully.
• Any questions about req and res parameters?
• The authors routes demonstrate the use of next
  • Calling next() runs the code for the next route that matches. (e.g., /authors/105)
• You can also provide a list of blocks. In this case, next() invokes the next block in the list.
  • See /cars/150
• If next() is called on the last handler on the list, then move to the next matching route.
• These blocks can also be defined as separate functions and used with multiple routes.
  • See /dogs and numbersOnly
  • See /colors and both numbersOnly and evensOnly
• This is how we can enforce logins in frameworks like Express
  • See https://github.com/kurmasz-SampleCode/CIS371-SampleCode/tree/master/ExpressSession
• There is one short-cut: use.
  • use applies the block to every route.
  • Things like app.use(bodyParser.urlencoded({ extended: true })) and app.use(session({...}) are just hooks that cause “setup” code to run before a routes “primary” block is run.
    • e.g., parse the request for post parameters, check the session cookie, etc.