Middleware and route configurations are very similar in Express. Route configurations are a specialized type of middleware based around Express' router object. Unlike Express route configurations, custom middleware can take any properties we want. Custom middleware acts as a closure that associates your custom parameters with Express's callback to handle the request:
middleware: function (params) { return function (req, res, next) { // this call back use both params & Express objects }}
By placing our middleware in Express's app.use method, we are wiring our middleware to a route in the same manner as our Express route configurations. We can also take this a step farther by nesting our middleware in an existing app.use configuration: ...
