Express is a routing and middleware web framework that has minimal functionality of its own: An Express application is essentially a series of middleware function calls. Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. The next middleware function is commonly denoted by a variable named next. Middleware functions can perform the following tasks: Execute any co

req.path Contains the path part of the request URL. // example.com/users?sort=desc req.path // => "/users" When called from a middleware, the mount point is not included in req.path. See app.use() for more details.

When you run Express apps for production, it is helpful to use a process manager to achieve the following tasks: Restart the app automatically if it crashes. Gain insights into runtime performance and resource consumption. Modify settings dynamically to improve performance. Control clustering. A process manager is somewhat like an application server: it’s a “container” for applications that facilitates deployment, provides high availability, and enables you to manage the application at runtim

app.get(path, callback [, callback ...]) Routes HTTP GET requests to the specified path with the specified callback functions. For more information, see the routing guide. You can provide multiple callback functions that behave just like middleware, except these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there’s no reason to proceed with the current route.

res.append(field [, value]) res.append() is supported by Express v4.11.0+ Appends the specified value to the HTTP response header field. If the header is not already set, it creates the header with the specified value. The value parameter can be a string or an array. Note: calling res.set() after res.append() will reset the previously-set header value. res.append('Link', ['<http://localhost/>', '<http://localhost:3000/>']); res.append('Set-Cookie', 'foo=bar; Path=/; HttpOnly'); re

req.originalUrl req.url is not a native Express property, it is inherited from Node’s http module. This property is much like req.url; however, it retains the original request URL, allowing you to rewrite req.url freely for internal routing purposes. For example, the “mounting” feature of app.use() will rewrite req.url to strip the mount point. // GET /search?q=something req.originalUrl // => "/search?q=something"

req.stale Indicates whether the request is “stale,” and is the opposite of req.fresh. For more information, see req.fresh. req.stale // => true

res.status(code) Sets the HTTP status for the response. It is a chainable alias of Node’s response.statusCode. res.status(403).end(); res.status(400).send('Bad Request'); res.status(404).sendFile('/absolute/path/to/404.png');

req.ip Contains the remote IP address of the request. When the trust proxy setting does not evaluate to false, the value of this property is derived from the left-most entry in the X-Forwarded-For header. This header can be set by the client or by the proxy. req.ip // => "127.0.0.1"

app.all(path, callback [, callback ...]) This method is like the standard app.METHOD() methods, except it matches all HTTP verbs. It’s useful for mapping “global” logic for specific path prefixes or arbitrary matches. For example, if you put the following at the top of all other route definitions, it requires that all routes from that point on require authentication, and automatically load a user. Keep in mind that these callbacks do not have to act as end-points: loadUser can perform a task, t