Request and Response object both are the callback function parameters and are used for Express.js and Node.js. 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.

Topics Covered

  • Request object
  • Request object properties
  • Request object methods
  • Response object
  • Response object properties
  • Response object methods

Request object

Express.js  is a  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:

S.No Properties Description
1 Used to hold a reference to the instance of the express application.
2 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.
3 req.cookies This property contains cookies sent by the request, used for the cookie-parser middleware.
4 req.ip req.ip is remote IP address of the request.
5 req.path req.path contains the path part of the request URL.
6 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 :

// => ?text/html?


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

Example :

// => "text/plain"  
// => "text/plain"  
// => undefined

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'html');'text/html');'text/*');  
// => true

req.param(name [, defaultValue])

 req.param method is used to fetch the value of param name when present.

Example :

// ?name=sonia  
         // => "sonia"  
         // POST name=sonia
         // => "sonia"  
         // /user/soniafor /user/: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

S.No properties Description
1 is hold a reference to the instance of the express application that is using the middleware.
2 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: '', path: '/admin', secure: true });  
res.cookie('Section', { Names: [sonica,riya,ronak] });  
res.cookie('Cart', { items: [1,2,3] }, { maxAge: 900000 });

Response Download Method

Syntax: [, filename] [, fn])  

Example:'/report-12345.pdf'); 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 :


Response Get Method

Syntax :   res.get(field)  

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

Example :


Response JSON Method

Syntax :   res.json([body])  

Response JSON method returns the response in JSON format.

Example :

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  


// 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(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:

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