Properties and Methods of Request and Response Objects in Express

Request and Response objects both are the callback function parameters and are used for Express and Node. You can get the request query, params, body, headers, and cookies. It can overwrite any value or anything there. However, overwriting headers or cookies will not affect the output back to the browser.

The following are the topics to be covered:

Request Object:

Express uses request & response objects parameters of the callback function and are used for the Express applications. The request object represents the HTTP request and contains properties for the request query string, parameters, body, HTTP headers, etc.

Syntax :

app.get(‘/’, function (req, res) { })  

Request Object Properties:

These properties are represented below:

Properties	Description
req.app	Used to hold a reference to the instance of the express application.
req.body	Contains key-value pairs of data submitted in the request body. By default, it is undefined and is populated when you use body-parsing middleware such as body-parser.
req.cookies	This property contains cookies sent by the request, used for the cookie-parser middleware.
req.ip	req.ip is remote IP address of the request.
req.path	req.path contains the path part of the request URL.
req.route	req.route is currently-matched route.

Request Object Methods:

There are various types of request object method, these methods are represented below: req.accepts (types). It is used to the check content types are acceptable, based on the request accept HTTP header field.

Example:

req.accepts('html');  
//=>?html?  
req.accepts('text/html');  
// => ?text/html?
req.get(field)

req.get(): req.get is used to returns the specified HTTP request header field.

Example:

req.get('Content-Type');  
// => "text/plain"  
req.get('content-type');  
// => "text/plain"  
req.get('Something');  
// => undefined
req.is(type)

If the incoming request is “CONTENT-TYPE”, this method returns true. HTTP header field matches the MIME type by the type parameter.

Example: // With Content-Type: text/html; charset=utf-8

req.is('html');  
req.is('text/html');  
req.is('text/*');  
// => true

req.param(name [, defaultValue]): req.param method is used to fetch the value of param name when present

Example:

// ?name=sonia  
req.param('name') 
// => "sonia"  
// POST name=sonia
req.param('name')  
// => "sonia"  
// /user/soniafor /user/:name   
req.param('name') 
// => "sonia"

Response Object:

The response object specifies the HTTP response when an Express app gets an HTTP request. The response is sent back to the client browser and allows you to set new cookies value that will write to the client browser.

Response Object Properties:

Properties	Description
res.app	res.app is hold a reference to the instance of the express application that is using the middleware.
res.locals	Specify an object that contains response local variables scoped to the request.

Response Object Method:

There are various types of response object method, these methods are represented below :

Response Append Method:

Syntax:

res.append(field, [value])  

Response append method appends the specified value to the HTTP response header field. That means if the specified value is not appropriate so this method redress that.

Example :

res.append('Link', ['<http://localhost/>', '<http://localhost:3000/>']);  
res.append('Warning', '299 Miscellaneous warning');

Response Attachment Method:

Syntax:

res.attachment(‘path/to/js_pic.png’);  

Response attachment method allows you to send a file as an attachment in the HTTP response.

Example:

res.attachment('path/to/js_pic.png');  

Response Cookie Method:

Syntax:

res.cookie(name, value [, options])  

It is used to set a cookie name to value. The value can be a string or object converted to JSON.

Example:

res.cookie('name', 'alish', { domain: '.google.com', path: '/admin', secure: true });  
res.cookie('Section', { Names: [sonica,riya,ronak] });  
res.cookie('Cart', { items: [1,2,3] }, { maxAge: 900000 });
Response Download Method
Syntax:   res.download(path [, filename] [, fn])  

Example:

res.download('/report-12345.pdf');

res.download method is transfer file at path as an “attachment” and the browser to prompt user for download.

Response End Method:

Syntax:

res.end([data] [, encoding])  

Response end method is used to end the response process.

Example:

res.end();  
res.status(404).end();
Response Get Method
Syntax :   res.get(field)  

res.get method provides HTTP response header specified by field.

Example:

res.get('Content-Type');
Response JSON Method
Syntax :   res.json([body])  

Response JSON method returns the response in JSON format.

Example :

res.json(null)  
res.json({ name: 'alish' })
Response Render Method
Syntax :   res.render(view [, locals] [, callback])  

Response render method renders a view and sends the rendered HTML string to the client.

Example :

// send the rendered view to the client  
res.render('index');  
// pass a local variable to the view  
res.render('user', { name: 'monika' }, function(err, html) {  
 // ...  
});

Response Status Method:

Syntax:

res.status(code)  

res.status method sets an HTTP status for the response.

Example: res.status(403).end():

res.status(400).send('Bad Request');

Response Type Method:

Syntax:

res.type(type)  

res.type method sets the content-type HTTP header to the MIME type.

Example:

res.type('.html');              // => 'text/html'  
res.type('html');               // => 'text/html'  
res.type('json');               // => 'application/json'  
res.type('application/json');   // => 'application/json'  
res.type('png');                // => image/png: