What is Node.Js Modules?

Module in Node.js is a simple or complex functionality organized in single or multiple JavaScript files which can be reused throughout the Node.js application.

Each module in Node.js has its own context, so it cannot interfere with other modules or pollute global scope. Also, each module can be placed in a separate .js file under a separate folder.

Module Types

Node.js includes three types of modules:

Core Modules

Local Modules

Third Party Modules

Core Modules

The core modules include minimum functionalities of Node.js. These core modules are compiled into its binary distribution and load automatically when Node.js process starts. However, you need to import the core module first in order to use it in your application.

File Name :

The following table lists some of the important core modules in Node.js.

http :- http module includes classes, methods and events to create Node.js http server.
url :-url module includes methods for URL resolution and parsing.
querystring :-querystring module includes methods to deal with query string.
path :-path module includes methods to deal with file paths.
fs :-fs module includes classes, methods, and events to work with file I/O.
util :- util module includes utility functions useful for programmers.

Loading Core Modules

you first need to import it using require() function

var module = require('my_module_name');

specify the module name in the require() function. The require() function will return an object, function, property or any other JavaScript type, depending on what the specified module returns.

Example

File Name : example.js

var http = require('http');
var server = http.createServer(function(req, res){
//write code here
});
server.listen(8080);

require() function returns an object because http module returns its functionality as an object, you can then use its properties and methods using dot notation e.g. http.createServer().

HTTP Module

Node.js has a built-in module called HTTP, which allows Node.js to transfer data over the Hyper Text Transfer Protocol (HTTP). To include the HTTP module, use the require() method:

The Node.js framework is mostly used to create web server based applications. The node.js used to create web servers which can serve content to users.

If a request is made through the browser on this port no 8080, then server application will send a ‘result’ response to the client.

var http = require('http');

Add an HTTP Header

If the response from the HTTP server is to be displayed as HTML, you should include an HTTP header with the correct content type:

File Name : sana.js

var http = require('http');

http.createServer(function (req, res) {
// add a HTTP header:
res.writeHead(200, {'Content-Type': 'text/html'});
res.write('Hello Sana!');
res.end();
}).listen(8080);

The first argument of the res.writeHead() method is the status code, 200 means that all is OK, the second argument is an object containing the response headers.

File Name :

Create Your Own Modules

ou can create your own modules.

File Name : myfirstmodule.js

Create a module that returns the current date and time:
exports.myDateTime = function () {
return Date();
};
Use the exports keyword to make properties and methods available outside the module file.

Include Your Own Module

The HTTP module can create an HTTP server that listens to server ports and gives a response back to the client. Use the createServer() method to create an HTTP server:

The function passed into the http.createServer() method, will be executed when someone tries to access the computer on port 8080.

var http = require('http');
var dt = require('./myfirstmodule');

http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write("The date and time are currently: " + dt.myDateTime());
res.end();
}).listen(8080);

Read the Query String

The function passed into the http.createServer() has a req argument that represents the request from the client, as an object

This object has a property called "url" which holds the part of the url that comes after the domain name:

File Name : sana.js

var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write(req.url);
res.end();
}).listen(8080);

Split the Query String

var http = require('http');
var url = require('url');

http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
var q = url.parse(req.url, true).query;
var txt = q.year + " " + q.month;
res.end(txt);
}).listen(8080);

GET Requests in Node.js

GET Request to get the data from another site in Node.js. To make a Get request in the node.js, we need to first have the request module installed.

npm install request

We are making a GET Request to www.ittutorial.in and subsequently calling a function when a response is received. When a response is received the parameters(error, response, and body) will have the following values

Error – In case there is any error received when using the GET request, it will be recorded here.

Response- The response will have the http headers which are sent back in the response.

Body- The body will contain the entire content of the response sent by ittutorial.

In this, we are just writing the content received in the body parameter to the console.log file. So basically, whatever we get by going to www.ittutorial.in will be written to the console.log.

File Name :

var request = require("request");
request("http://www.ittutorial.in",function(error,response,body)
{
console.log(body);
});

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