let module = require('module_name')\r\n<\/pre>\nThe return type of require() function depends on what the particular module returns.<\/p>\n
Http, file system and url modules are some of the core modules. We will be discussing this in the latter part of this blog.<\/p>\n
2. Nodejs Local Modules:<\/h4>\n
Local modules are created by us locally in our Node.js application. These modules are included in our program in the same way as we include the built in module.<\/p>\n
Let’s build a module with the name as sum to add two numbers and include them in our index.js file to use them.<\/p>\n
Code for creating local modules and exporting:<\/strong><\/p>\nexports.add=function(n,m){\r\n return n+m;\r\n};\r\n<\/pre>\nExports keyword is used to make properties and methods available outside the file.<\/p>\n
In order to include the add function in our index.js file we use the require function.<\/p>\n
Code for including local modules:<\/strong><\/p>\nlet sum = require('.\/sum')\r\n \r\nconsole.log(\"Sum of 10 and 20 is \", sum.add(10, 20))\r\n<\/pre>\nAdd the above code in a index.js file<\/p>\n
To run this file, open a terminal in the project directory and type node index.js and press enter. You can see the result of addition of 10 and 20. This addition has been performed by the add function in the sum module.<\/p>\n
<\/p>\n
3. Nodejs Third Party Modules:<\/h4>\n
Modules that are available online and are installed using the npm are called third party modules. Examples of third party modules are express, mongoose, etc.<\/p>\n
To install third party modules refer to the previous blog where we have discussed how to install modules using npm.<\/p>\n
Nodejs HTTP Module:<\/h3>\n
It is a built-in module of node.js. It allows node.js applications to transfer data using HyperText Transfer Protocol (HTTP).<\/p>\n
This module creates an HTTP server that listens to server ports and also gives responses back to the client.<\/p>\n
Properties:<\/h4>\n
1. http.METHODS:<\/strong> this tells us all the methods available in http module.<\/p>\nCode to check HTTP methods:<\/strong><\/p>\nlet http = require('http');\r\nconsole.log(http.METHODS)\r\n<\/pre>\nOutput:<\/strong><\/p>\n![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-http-methods.png\")
<\/a><\/p>\n2. http.STATUS_CODES:<\/strong> It tells us all the status codes and its description.<\/p>\nCode to check HTTP status codes:<\/strong><\/p>\nlet http = require('http');\r\nconsole.log(http.STATUS_CODES)\r\n<\/pre>\nOutput:<\/strong><\/p>\n![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-http-statuscode.png\")
<\/a><\/p>\nMETHODS:<\/h4>\n
CREATE SERVER:<\/strong> We can use it to create a server. The create server will take a function which will run when we try to access the port.<\/p>\nlisten()<\/strong> starts the HTTP server and listens for connections.<\/p>\nBelow code sets up a server which we can access when we visit localhost:3000<\/p>\n
Code for creating http server:<\/strong><\/p>\nlet http = require('http');\r\nhttp.createServer(function (req, res) {\r\n res.write('Welcome to DataFlair!');\r\n res.end();\r\n}).listen(3000);\r\n<\/pre>\nNow visit localhost:3000, you will see the message<\/p>\n
![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-http-output.png\")
<\/a><\/p>\nAdding HTTP header:<\/h4>\n
If the message from the server needs to be shown as an HTML, then we have to include content type in the header.<\/p>\n
Code for adding http header:<\/strong><\/p>\nvar http = require('http');\r\nhttp.createServer(function (req, res) {\r\n res.writeHead(200, { 'Content-Type': 'text\/html' });\r\n res.write('Hello from DataFlair!');\r\n res.end();\r\n}).listen(3000);\r\n<\/pre>\nReading query string:<\/h4>\n
The function in the create server has a request argument and this request object has a property of URL. It contains the part of the url that is present after the domain name.<\/p>\n
So when you go to localhost:3000\/dataflair\/nodejs, the output will be dataflair\/nodejs<\/p>\n
Code for reading query string:<\/strong><\/p>\nvar http = require('http');\r\nhttp.createServer(function (req, res) {\r\n res.writeHead(200, { 'Content-Type': 'text\/html' });\r\n res.write(req.url);\r\n res.end();\r\n}).listen(3000);\r\n<\/pre>\nNodejs URL Module:<\/h3>\n
This is a built-in module of node.js. It breaks down the url into readable parts. It is included in the file by using the require function;<\/p>\n
To Parse an address, use the url.parse() method. It will return a URL object with each part of the address as its properties.<\/p>\n
Code for using the url Module:<\/strong><\/p>\nlet url = require('url');\r\nvar adr = 'http:\/\/localhost:3000\/search?year=2021&month=august';\r\nvar q = url.parse(adr, true);\r\n \r\nconsole.log(q.host);\r\nconsole.log(q.pathname);\r\nconsole.log(q.search);\r\n \r\nvar qdata = q.query;\r\nconsole.log(qdata.month);\r\n<\/pre>\nOUTPUT<\/strong><\/p>\n![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-url-module.png\")
<\/a><\/p>\nIn the above image you can see that the url has been parsed and individual parts are shown in the console.<\/p>\n
File Server:<\/h4>\n
Now we will be parsing the url and based on it we will be returning the content of the requested file. If the file is not found we will get an 404 error message. So first create a html\/text file and add some content. We have made a text file with name as \u201cDataFlair.txt\u201d and it contains the line \u201cWelcome to DataFlair\u201d .<\/p>\n
Code for serving a file over http:<\/strong><\/p>\nvar http = require('http');\r\nvar url = require('url');\r\nvar fs = require('fs');\r\n \r\nhttp.createServer(function (req, res) {\r\n var q = url.parse(req.url, true);\r\n var filename = \".\" + q.pathname;\r\n fs.readFile(filename, function (err, data) {\r\n if (err) {\r\n res.writeHead(404, { 'Content-Type': 'text\/html' });\r\n return res.end(\"404 Not Found\");\r\n }\r\n res.writeHead(200, { 'Content-Type': 'text\/html' });\r\n res.write(data);\r\n return res.end();\r\n });\r\n}).listen(3000);\r\n<\/pre>\nNow go to http:\/\/localhost:3000\/DataFlair.txt you will get the contents present in the file.<\/p>\n
Output:<\/strong><\/p>\n![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-file-server-output.png\")
<\/a><\/p>\nNodejs File System Module:<\/h4>\n
This is a built-in module of node.js. It helps to create, read, write, update, or delete files in our computer. It is included in the file by using the require function.<\/p>\n
Create File: It has mainly 3 methods<\/h4>\n
1. Append file.<\/strong><\/p>\nThe fs.appendFile() method\u2019s second argument takes the text that we want to append, and then it appends at the end of the file, if the given file does not exist then the file will be created.<\/p>\n
Code for appending text in a file:<\/strong><\/p>\nvar fs=require(\u2018fs\u2019)\r\nfs.appendFile('DataFlairDemo.txt', 'welcome to DataFlair', function (err) {\r\n if (err) throw err;\r\n console.log('Saved!');\r\n});\r\n<\/pre>\nOUTPUT<\/strong><\/p>\n![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-fs-append-file.png\")
<\/a><\/p>\n2. Open file<\/strong><\/p>\nThe fs.open() method\u2019s second argument is “w” for “writing”,which indicates that the file is opened for writing and if it does not exist then an empty file is created.<\/p>\n
Code for opening a file:<\/strong><\/p>\nvar fs=require(\u2018fs\u2019)\r\nfs.open('DataFlairDemo.txt', 'w', function (err, file) {\r\n if (err) throw err;\r\n console.log('Saved!');\r\n});\r\n<\/pre>\nOUTPUT<\/strong><\/p>\n![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-fs-openfile.png\")
<\/a><\/p>\nYou can see that a file has been added.<\/p>\n
3. WriteFile:<\/strong><\/p>\nThe fs.writeFile() method\u2019s second argument takes the text that we want to write, and then it overrides the content available in the file if the given file does not exist then the file will be created.<\/p>\n
Code for writing in a file:<\/strong><\/p>\nvar fs = require('fs');\r\nfs.writeFile('DataFlairDemo.txt', 'Learn Node.js from DataFlair', function (err, file) {\r\n if (err) throw err;\r\n console.log('Saved!');\r\n});\r\n<\/pre>\nOUTPUT<\/strong><\/p>\n![\"nodejs](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/09\/nodejs-fs-wrtefile.png\")
<\/a><\/p>\nUpdate File: It has mainly 2 methods<\/h4>\n
1) fs.appendFile()<\/strong><\/p>\nThe fs.appendFile() method\u2019s second argument takes the text that we want to append, and then it appends at the end of the file, if the given file does not exist then the file will be created.<\/p>\n
Code for fs.appendFile()<\/strong><\/p>\nvar fs=require(\u2018fs\u2019)\r\nfs.appendFile('DataFlairDemo.txt', 'welcome to DataFlair', function (err) {\r\n if (err) throw err;\r\n console.log('Saved!');\r\n});\r\n<\/pre>\nOutput<\/strong><\/p>\n<\/a><\/p>\n2) fs.writeFile():<\/strong><\/p>\nThe fs.writeFile() method\u2019s second argument takes the text that we want to write, and then it overrides the content available in the file, if the given file does not exist then the file will be created.<\/p>\n
Code for writing in a file:<\/strong><\/p>\nvar fs = require('fs');\r\nfs.writeFile('DataFlairDemo.txt', 'Learn Node.js from DataFlair', function (err, file) {\r\n if (err) throw err;\r\n console.log('Saved!');\r\n});\r\n<\/pre>\nOUTPUT<\/strong><\/p>\n<\/a><\/p>\nRead File:<\/h4>\n
It is used to read files present in your system.<\/p>\n