res.json([body]) Sends a JSON response. This method is identical to res.send() with an object or array as the parameter. However, you can use it to convert other values to JSON, such as null, and undefined (although these are technically not valid JSON). res.json(null); res.json({ user: 'tobi' }); res.status(500).json({ error: 'message' });

req.ips When the trust proxy setting does not evaluate to false, this property contains an array of IP addresses specified in the X-Forwarded-For request header. Otherwise, it contains an empty array. This header can be set by the client or by the proxy. For example, if X-Forwarded-For is client, proxy1, proxy2, req.ips would be ["client", "proxy1", "proxy2"], where proxy2 is the furthest downstream.

res.attachment([filename]) Sets the HTTP response Content-Disposition header field to “attachment”. If a filename is given, then it sets the Content-Type based on the extension name via res.type(), and sets the Content-Disposition “filename=” parameter. res.attachment(); // Content-Disposition: attachment res.attachment('path/to/logo.png'); // Content-Disposition: attachment; filename="logo.png" // Content-Type: image/png

req.params This property is an object containing properties mapped to the named route “parameters”. For example, if you have the route /user/:name, then the “name” property is available as req.params.name. This object defaults to {}. // GET /user/tj req.params.name // => "tj" When you use a regular expression for the route definition, capture groups are provided in the array using req.params[n], where n is the nth capture group. This rule is applied to unnamed wild card matches with string

app.put(path, callback [, callback ...]) Routes HTTP PUT 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 that 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 r

app.disable(name) Sets the Boolean setting name to false, where name is one of the properties from the app settings table. Calling app.set('foo', false) for a Boolean property is the same as calling app.disable('foo'). For example: app.disable('trust proxy'); app.get('trust proxy'); // => false

app.render(view, [locals], callback) Returns the rendered HTML of a view via the callback function. It accepts an optional parameter that is an object containing local variables for the view. It is like res.render(), except it cannot send the rendered view to the client on its own. Think of app.render() as a utility function for generating rendered view strings. Internally res.render() uses app.render() to render views. The local variable cache is reserved for enabling view cache. Set it to

router.METHOD(path, [callback, ...] callback) The router.METHOD() methods provide the routing functionality in Express, where METHOD is one of the HTTP methods, such as GET, PUT, POST, and so on, in lowercase. Thus, the actual methods are router.get(), router.post(), router.put(), and so on. You can provide multiple callbacks, and all are treated equally, and behave just like middleware, except that these callbacks may invoke next('route') to bypass the remaining route callback(s). You can use

Routing refers to determining how an application responds to a client request to a particular endpoint, which is a URI (or path) and a specific HTTP request method (GET, POST, and so on). Each route can have one or more handler functions, which are executed when the route is matched. Route definition takes the following structure: app.METHOD(PATH, HANDLER) Where: app is an instance of express. METHOD is an HTTP request method. PATH is a path on the server. HANDLER is the function executed

app.enable(name) Sets the Boolean setting name to true, where name is one of the properties from the app settings table. Calling app.set('foo', true) for a Boolean property is the same as calling app.enable('foo'). app.enable('trust proxy'); app.get('trust proxy'); // => true