Have you ever wondered what the req and res objects in Express actually are?
req
An extended instance of the Node.js core http.IncomingMessage class:
/**
 * Request prototype.
 * @public
 */
var req = Object.create(http.IncomingMessage.prototype)
(Source: expressjs/express/lib/request.js#L26-L31)
res
An extended instance of the Node.js core http.ServerResponse class:
/**
 * Response prototype.
 * @public
 */
var res = Object.create(http.ServerResponse.prototype)