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  • Node http server

  • Connect

    • Connect is an extensible HTTP server framework for node using "plugins" known as middleware.
    • Allows you to "plugin" handlers into the (req, res) => { res.end(); } server function using .use()
    • connect() create function (req, res) => {} that can be used with http.createServer()
  • Express

  • Middleware

    • Add handlers to the stack with .use(handler)
    • There can (and will) be multiple handlers!
    • A handler can be asynchronous and take longer to finish!
    • How to know if a handler fully served the request?
      • Either call res.end() (we're done) or next() (nah, let the next handler do stuff)
      • Some response methods implicitly end the request, like .json(), .sendFile(), etc.
    • async (req, res) is a major fail!!!
      • Assume the handler actually calls res.end()
      • What happens if the handler throws an error? Who will notice?
        • Unhandled promise rejection AND dangling request!!!
      • Always do async (req, res, next) => { try { ... } catch (error) { next(error); } } to catch async errors!
      • Express v5 (currently alpha) will supoprt async handlers
  • Middleware stack

    • Add multiple handlers at once with .use(handler1, handler2, [handler3, handler4])
    • The middleware stack is traversed until someone calls res.end()
      • If noone ends the request, it will stay dangling!
    • Make a handler only handle a certain path with .use(path, handler)
    • Make a handler only handle a certain method with .METHOD(handler)
    • Mix and match
    • Order is important!!!
    • You can even add multiple handlers for the exact same method and path
    • Call next("route") to end handling for the current route
  • Not found handling

    • What happens if no handler matches the current request?
    • Request would stay dangling
    • Add a special handler to the end of your stack!
    • Express automatically adds a 404 handler, but its very simple (Cannot ${method} ${path})
  • Error handling

    • Handlers are async... What if an error occurs inside the app logic? Where to put it?
    • Just call next(error)
    • The app will continue to traverse the middleware stack until it finds an error handler
    • Error handlers have signature (error, req, res, next) => {} (handler.length is 4 instead of 2 or 3)
    • Allows for central error handling (i.e. logging, output the stack, error response format, ...)
    • Express automatically adds an error handler, but its very simple (res.send(error.message))
  • Router/Sub-Apps

    • Create a sub-app with express.Router
    • express() is in fact a router, with extra functionallity
    • You could also do app.use(express()) to mount a complete express app
    • Calling next("router") will end handling for the current router


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