After reading this Node.js tutorial, you should be able to build applications using Node.js and deploy it on a cloud server. Let’s begin.<\/p>\n
Step 1: Node js basic concepts<\/h2>\n
Node.js runs on top of V8\u2014Chrome runtime engine\u2014that compiles the JavaScript code in the native machine code (one of the reasons why Google Chrome runs fast and consumes a lot of memory), followed by the custom C++ code. <\/p>\n
The original version has 8,000 lines of code (LOC)\u2014and then, the standard libraries for programmers. The following is the figure of Node.js architecture: <\/p>\n
![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/2017\/08\/Nodejs-Architecture.png\")
<\/p>\n
V8<\/h3>\n
The V8 JavaScript engine is an open-source JavaScript engine developed for the Chrome project. The innovation behind V8 is that it compiles the JavaScript code in native machine code and executes it. <\/p>\n
The developers of V8 used the just-in-time (JIT) compiler methodology to improve the code compilation time. It is open-source and is used in the Node.js and MongoDB project.<\/p>\n
Link: https:\/\/github.com\/v8\/v8<\/a><\/p>\n The libuv library is a cross-platform library that provides an asynchronous I\/O facility by enabling an event-driven I\/O operation. The libuv library creates a thread for the I\/O operation (file, DNS, HTTP, and so on) and returns a callback. <\/p>\n Upon completion of the particular I\/O operation, it returns the events so that the callee program does not have to wait for the completion of the I\/O operation. <\/p>\n As I mentioned earlier, libuv assigns threads for the I\/O operation and returns the callback to the callee program. Therefore, Node.js internally creates threads for I\/O operation; however, it gives the programmer access to a single runtime thread. In this way, things are simple and sweet: <\/p>\n When you make an HTTP request to the web server built using Node. It creates the libuv thread and is ready to accept another request. <\/p>\n As soon as the events are triggered by libuv, it returns the response to the user. The libuv library provides the following important core features:<\/p>\n The libuv library internally uses another famous library called libeio<\/strong>, which is designed for threading<\/strong> and asynchronous I\/O<\/strong> events and libev, which is a high-performance event loop. <\/p>\n Therefore, you can treat libuv as a package wrapper for both of them. <\/p>\n Let\u2019s learn a little bit about multi-threading and single threading.<\/p>\n The multi-threading approach provides parallelism using threads so that multiple programs can simultaneously run. <\/p>\n it is really difficult to handle concurrency and deadlock in a multi-threading system. <\/p>\n On the other hand, with single-threading, there is no chance of deadlock in the process, and managing the code is also easy. You can still hack and busy the event loop for no reason; however, that’s not the point. <\/p>\n Consider the following working diagram that is developed by StrongLoop\u2014one of the core maintainers of Node.js: <\/p>\n Node.js uses single-threading for runtime environment; however, internally, it does create multiple threads for various I\/O operations. <\/p>\n It doesn’t imply that it creates threads for each connection, libuv contains the Portable Operating System Interface (POSIX) system calls for some I\/O operations. <\/p>\n Multi-threading blocks the I\/O until the particular thread completes its operation and results in overall slower performance.<\/p>\n Consider the following image: <\/p>\n If the single-threading programs work correctly, they will never block the I\/O and will be always ready to accept new connections and process them.<\/p>\n As you can see in the image earlier, I\/O does not get blocked by any thread in Node.js. Then, how does it notify particular processes that the task has been done or an error has occurred? <\/p>\n Node.js is asynchronous<\/strong> in nature and you need to program it in an asynchronous way, which you cannot do unless you have a clear understanding of the event loop. <\/p>\n If you know how the event loop works, you will no longer get confused and hopefully, never block the event loop.<\/p>\n The Node.js runtime system has an execution stack<\/strong>, where it pushes every task to execute. <\/p>\n The operating system pops the task from the execution stack and conducts the necessary action required to run the task. <\/p>\n To run the asynchronous<\/strong> code, this approach won’t work. The libuv library introduces a queue that stores the callback for each asynchronous operation. <\/p>\n Event loop runs on a specific interval, which is called tick<\/strong> in the Node.js terminology and checks the stack. <\/p>\n If the stack is empty, it takes the callback from the queue and pushes it in the stack for execution, as shown in the following figure: <\/p>\n The libuv library creates the thread and returns the callback to us. <\/p>\n As it’s an asynchronous operation, it goes to the queue instead of the stack and the event loop fetches it when the stack is empty and does the execution. You can validate the same concept using the setTimeout() function.<\/p>\n Consider the following code: setTimeout(timeout() => { console.log('i am third'); If you run this code, you will get an output similar to the following: The reason is obvious, setTimeout()<\/strong> waits for five seconds and prints its output; however, that does not block the event loop. Let’s set the timer to 0 seconds and see what happens: <\/p>\n setTimeout(timeout() => { console.log('i am third'); The output is still the same: Why so? Even if you set the timer to 0, it goes in the queue; however, it is immediately processed as its time is 0 second. <\/p>\n The event loop recognizes that the stack is still not empty, that is, the third console was in process; therefore, it pushes the callback after the next tick of the event loop.<\/p>\n We have covered the basics of Node. Let’s proceed ahead with the installation in your operating system. If you already have Node installed, kindly skip this section.<\/p>\n To install Node in Windows Operating System, follow these steps:<\/p>\n Download the Node installer from the official site. <\/p>\n Run the installer and click Next until the setup wizard is complete. <\/p>\n Open command prompt or PowerShell and run the following command. To install Node in the Mac operating system, follow these steps:<\/p>\n Download the Node installer from the official site. <\/p>\n Run the installer and click Continue until the setup wizard is complete. Open the terminal and run the following command. To install Node in the Ubuntu operating system, open the terminal and run the following command one by one. <\/p>\n Then, Also, install the build tools. Update the NPM. Verify the installation, run the following command. It should return the version of Node installed in your system. In our case, it is V12.<\/p>\n Alright, let’s move to the next step.<\/p>\n Let’s build a simple Web application that returns a message as “Hello World” when user request the server. We will use the native HTTP<\/strong> module of Node to achieve the Web Server functionality. Here is the code: <\/p>\n server.listen(port, hostname, () => { Copy\/paste it in a new file. Name the file as hello.js and save it. <\/p>\n To run this code, open your terminal and switch to the location where you have stored the file. Run this command to execute your code. <\/p>\n You should have the following message on the terminal. <\/p>\n Open your browser and type localhost:3000 and hit enter. You should see the following message. <\/p>\n Congratulations!<\/p>\n You have just developed your first Node program. <\/p>\n Our server responds to a simple message as a text, however, in practice we need to handle different types of responses. <\/p>\n Let\u2019s look over some of the common response types.<\/p>\n One of the most common responses that you need to handle while developing a Node application is JSON. <\/p>\n Here is how you can send JSON responses.<\/p>\n server.listen(port, hostname, () => { If you run this code, and navigate to the browser, you should see the following response.<\/p>\n Let\u2019s look over how to send HTML as a response. <\/p>\n This is a HTML response<\/p>\n \" server.listen(port, hostname, () => { When you run this code, you should see the following response.<\/p>\n Awesome. <\/p>\n Let\u2019s go ahead and create different routes to support multiple responses. <\/p>\n Check out the code shown below.<\/p>\n \"); \"); server.listen(port, hostname, () => { As you can see, we are using switch cases to determine different routes and on each route, we are sending different responses to each route.<\/p>\n Navigate your browser to localhost:3000\/home<\/strong> to view the response.<\/p>\n Navigate your browser to localhost:3000\/about to view the second response.<\/p>\n Awesome. We built a simple web server in Node. Let’s jump to the next step.<\/p>\n Node modules are the basic building block of the Node program.<\/p>\n The node module is a set of functions that can be reused in your application.<\/p>\n Node has built-in modules as well as you can create your node modules. <\/p>\n Some of the famous built-in node modules are fs, net, http<\/strong>, and many of the popular modules such as express, nodemailer<\/strong> built on top of these built-in modules. <\/p>\n We can install node modules using the node package manager or called npm.<\/p>\n You can install node modules using the following command. <\/p>\n Open your terminal\/command prompt and run this command. <\/p>\n Or For example: You can also install the module and write it in your package.json file using the following command. <\/p>\n Or<\/p>\n You can use the following command to uninstall node modules. <\/p>\n If you want to remove the module entry from the package.json file, use this command. <\/p>\n You can create your own node module as well. All you need to do is create a function and export it for the reusability. <\/p>\n For example, consider this code which can act as a node module. <\/p>\n You can reuse this module in your code like this: <\/p>\n This is a really simple example. However, this gives an idea about how to create node modules. If you are interested in more detailed information, visit this tutorial.<\/a><\/p>\n Node modules are managed by the file called package.json<\/strong>. This file contains the list of the packages your project is using along with the version number etc. <\/p>\n A typical package.json<\/strong> file looks like this:<\/p>\n We also specify details such as project name, version, entry file of the project in the package.json.<\/p>\n All the dependencies that are installed using npm install command are listed in the package.json.<\/strong> You should always maintain the updated version of package.json while dealing with the packages. <\/p>\n Let’s jump to the next step.<\/p>\n The fs<\/strong> module provides an API for interacting with the file system of your operating system. To use this module, require it in your code like this: <\/p>\n There are lots of methods provided under this node module to perform various tasks such as creating files, writing data into a file, reading data from files, etc.<\/p>\n You can use fs.readFile()<\/strong> or fs.readFileSync()<\/strong> method to read files in Node.<\/p>\n For example: Using the readFile() method. <\/p>\n Using the readFileSync()<\/strong> method. <\/p>\n The simplest approach to check whether the file exists or not is by using the readFile()<\/strong> function. <\/p>\n However, this function does open the file descriptor and occupies some memory too. <\/p>\n If you just want to check the file existences in the system, I highly recommend the access()<\/strong> function. Here is the code: <\/p>\n The file system module provides three methods to create files:<\/p>\n fs.open() <\/strong>method opens a new file or creates a new empty file if it does not exist in the specified path. <\/p>\n It takes the second parameter which acts as a flag such as w for writing, w+ for reading and writing, etc. Code: <\/p>\n fs.writeFile() <\/strong> method allows you to create or replace files with the content. <\/p>\n If a file exists, it will replace the content with the provided content and if the file does not exist, it will create it. <\/p>\n fs.appendFile()<\/strong> method appends the provided content at the end of the file. <\/p>\n To delete a file, we can use fs.unlink()<\/strong> method. <\/p>\n To rename a file, we can use the fs.rename()<\/strong> method. <\/p>\n You can also copy files using the fs.copy() method.<\/p>\n <\/code><\/p>\n Let’s jump to the next step.<\/p>\n Express is a popular framework to develop web applications in Node. <\/p>\n Express is widely used and can be used to develop web applications such as Web Server, REST API Server, Streaming engine, etc. <\/p>\n In this section, we are going to learn about express and we will create a simple web server with different routes. <\/p>\n Terminologies we will use in this section are:<\/p>\n Let’s begin.<\/p>\n Create a new folder and switch to it using a terminal or command prompt. <\/p>\n Create a new node project using the following command.<\/p>\n This will create a sample package.json for your project. To install the express module, run the following command. <\/p>\n The latest version of the express framework will be installed in your project. Now create a new file and name it app.js. In this file, we will write our web server using express. <\/p>\n app.listen(process.env.port || 3000); <\/p>\n console.log('Web Server is listening at port '+ (process.env.port || 3000)); In the code shown above, we have required the express module and created a new instance of it. <\/p>\n In the end, we have started our Server using the listen()<\/strong> function.<\/p>\n Routers are simply an endpoint of a server. <\/p>\n For example, facebook.com\/codeforgeek, here the codeforgeek<\/strong> is a route. <\/p>\n We need to create routers in our web application to serve different requests. We will create the following routes in our web application.<\/p>\n Express routers allow us to serve different HTTP methods such as GET, POST, PUT, DELETE, HEAD. Here is how to create a router. <\/p>\n router.get('\/home', (req,res) => { router.get('\/profile', (req,res) => { router.get('\/login', (req,res) => { router.get('\/logout', (req,res) => { app.use('\/', router); <\/p>\n app.listen(process.env.port || 3000); <\/p>\n console.log('Web Server is listening at port '+ (process.env.port || 3000)); Let’s run our application, save the file, and run the code using the following command. <\/p>\n You should see the following message in the terminal. <\/p>\n Open your browser and visit the routes.<\/p>\n Here is the profile page. <\/p>\n You can also send HTML<\/a>\/JSON\/XML as a response.<\/p>\n Express provides middleware function support. Middleware functions as the name suggests can be used to make changes in the request\/response lifecycle of the express. There are five types of middleware functions in the express.<\/p>\n We can use middleware in the application object of the express. For example: <\/p>\n app.use((req, res, next) => { app.listen(process.env.port || 3000); <\/p>\n console.log('Web Server is listening at port '+ (process.env.port || 3000)); In a similar way as application middleware, we can use router middleware. For example: <\/p>\n router.use((req, res, next) => { router.get('\/home', (req,res) => { app.use('\/', router); console.log('Web Server is listening at port '+ (process.env.port || 3000)); We can use this middleware to catch errors. <\/p>\n Learn more about this function here<\/a>.<\/p>\n Express provides some middleware by default such as static, JSON, etc. <\/p>\n We can use third-party middlewares such as body-parser. Here is how we can install third-party middleware. <\/p>\n To use this middleware, we need to require our code and load it. <\/p>\n router.get('\/home', (req,res) => { router.get('\/profile', (req,res) => { router.get('\/login', (req,res) => { router.get('\/logout', (req,res) => { \/\/ add middleware before routes app.use('\/', router); <\/p>\n app.listen(process.env.port || 3000); <\/p>\n console.log('Web Server is listening at port '+ (process.env.port || 3000)); If you are interested in creating your middleware, I recommend you this article.<\/a><\/p>\n We can handle sessions in Express using express-session middleware. We can use this middleware to create, track, and delete sessions. <\/p>\n To use this module in our code, load this as a middleware. <\/p>\n Now, we can use req.session<\/strong> object to create, track, and delete sessions. <\/p>\n To learn more about the session, please read this<\/a> article.<\/p>\n We can also use external stores such as Redis to store session values instead of storing them in memory. <\/p>\n Let’s jump to the next step and learn about the integration of databases with Node.<\/p>\n The database is an integral part of any application. You must know how to use it with Node to build a complete application. <\/p>\n We are going to cover the following databases in this section:<\/p>\n Let\u2019s begin with MySQL.<\/p>\n MySQL is a very popular SQL database. In this section, we will learn how to connect, query, and use it with NodeJS.<\/p>\n MySQL is a very popular database and has been used in millions of applications. We can use MySQL with Node as well. <\/p>\n We need to install the module name as MySQL to use it with the MySQL database.<\/p>\n You need to have the MySQL database installed in your system before proceeding.<\/p>\n To install the node module to connect with MySQL: <\/p>\n Here is how we can establish a connection to the MySQL engine. <\/p>\n const pool = mysql.createPool({ pool.query(\"SELECT * from You can execute the queries such as INSERT, UPDATE and DELETE in a similar fashion. Learn more in detail about using Node and MySQL<\/a>.<\/p>\n Let\u2019s learn about MongoDB.<\/p>\n MongoDB is a very popular NoSQL database. Learn how to connect, query, and use it with NodeJS.<\/p>\n MongoDB is one of the most popular general-purpose NoSQL database engines. <\/p>\n To integrate MongoDB with Node, you need to install the MongoDB database in your system. <\/p>\nEvent driven I\/O \u2013 libuv<\/h3>\n
Working of libuv \u2013 the core of Node.js<\/h3>\n
![\"how](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2019-05-23-at-4.07.50-AM.png\")
<\/p>\n\n
![\"Multithreading](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2019-05-23-at-4.13.53-AM.png\")
<\/p>\n![\"Single](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2019-05-23-at-4.14.44-AM.png\")
<\/p>\nImportance of event loop<\/h3>\n
How Event Loop Works<\/h3>\n
![\"How](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2019-05-23-at-4.18.31-AM.png\")
<\/p>\n
\n
\nconsole.log('i am first');<\/p>\n
\n console.log('i am second');
\n}, 5000); <\/p>\n
\n<\/code><\/p>\n
\n
\ni am first
\ni am third
\ni am second
\n<\/code><\/p>\n
\nconsole.log('i am first');<\/p>\n
\n console.log('i am second');
\n}, 0);<\/p>\n
\n<\/code><\/p>\n
\n
\ni am first
\ni am third
\ni am second
\n<\/code><\/p>\nInstalling Node in Your Operating System<\/h3>\n
\n
\nnode -v<\/code>
\nIt should return the node version. <\/p>\nnpm install -g npm<\/code>\n<\/ul>\n\n
\n![\"mac](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/mac-node-setup.png\")
<\/p>\n
\nnode -v<\/code>
\nIt should return the node version.<\/p>\nnpm install -g npm<\/code>\n<\/ol>\ncurl -sL https:\/\/deb.nodesource.com\/setup_12.x | sudo -E bash - <\/code><\/p>\n
\nsudo apt-get install -y nodejs<\/code><\/p>\n
\nsudo apt-get install -y build-essential<\/code><\/p>\n
\nsudo npm install -g npm<\/code><\/p>\n
\nnode -v<\/code><\/p>\nStep 2: Building a Simple Web Server in Node.js<\/h2>\n
\nconst http = require('http');
\nconst hostname = 'localhost';
\nconst port = 3000;
\nconst server = http.createServer((req, res) => {
\n res.statusCode = 200;
\n res.setHeader('Content-Type', 'text\/plain');
\n res.end('Hello World ');
\n}); <\/p>\n
\n console.log(`Server running at http:\/\/${hostname}:${port}\/`);
\n});
\n<\/code><\/p>\n
\nnode hello.js
\n<\/code><\/p>\n![\"Node](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2019-05-23-at-4.27.13-AM.png\")
<\/p>\n![\"Node](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2019-05-23-at-4.28.43-AM.png\")
<\/p>\n
\nconst http = require(\"http\");
\nconst hostname = \"localhost\";
\nconst port = 3000;
\nconst server = http.createServer((req, res) => {
\n res.statusCode = 200;
\n res.setHeader(\"Content-Type\", \"application\/json\");
\n res.end('{ \"message\" : \"Hello World \" }');
\n});<\/p>\n
\n console.log(`Server running at http:\/\/${hostname}:${port}\/`);
\n});
\n<\/code><\/p>\n![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2020-05-15-at-10.26.51-PM.png\")
<\/p>\n
\nconst http = require(\"http\");
\nconst hostname = \"localhost\";
\nconst port = 3000;
\nconst server = http.createServer((req, res) => {
\n res.statusCode = 200;
\n res.setHeader(\"Content-Type\", \"text\/html\");
\n res.end(
\n \"<\/p>\nHello World<\/h1>\n
\n
\n );
\n});<\/p>\n
\n console.log(`Server running at http:\/\/${hostname}:${port}\/`);
\n});
\n<\/code><\/p>\n![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2020-05-15-at-10.37.20-PM.png\")
<\/p>\n
\nconst http = require(\"http\");
\nconst hostname = \"localhost\";
\nconst port = 3000;
\nconst server = http.createServer((req, res) => {
\n res.statusCode = 200;
\n res.setHeader(\"Content-Type\", \"text\/html\");
\n switch (req.url) {
\n case \"\/home\":
\n res.writeHead(200);
\n res.end(\"<\/p>\nThis is Home page<\/h1>\n
\n break;
\n case \"\/about\":
\n res.writeHead(200);
\n res.end(\"<\/p>\nThis is About page<\/h1>\n
\n break;
\n default:
\n break;
\n }
\n});<\/p>\n
\n console.log(`Server running at http:\/\/${hostname}:${port}\/`);
\n});
\n<\/code><\/p>\n![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2020-05-15-at-10.46.49-PM.png\")
<\/p>\n![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/Screenshot-2020-05-15-at-10.46.58-PM.png\")
<\/p>\nStep 3: Node modules and NPM<\/h2>\n
\nnpm install
\n<\/code><\/p>\n
\n
\nnpm i
\n<\/code><\/p>\n
\n
\nnpm install express
\n<\/code><\/p>\nnpm install --save express<\/code><\/p>\nnpm i --S express<\/code><\/p>\nnpm remove npm remove --save
\nconst calc = (a,b,p) => {
\n if(a || b || p ) {
\n return \"Please provide all parameters\";
\n }
\n switch(p) {
\n case '+': {
\n return a+b;
\n break;
\n }
\n case '-': {
\n return a-b;
\n break;
\n }
\n case '*': {
\n return a*b;
\n break;
\n }
\n case '\/': {
\n return a\/b;
\n break;
\n }
\n default:{return;}
\n }
\n}
\nexports.calc=calc; \/\/very important line
\n<\/code><\/p>\n
\nvar dt = require('.\/mymodule');
\nconsole.log(dt.calc(10,20,'+'));
\n<\/code><\/p>\n
\n{
\n \"name\": \"codeforgeek-app-server\",
\n \"version\": \"1.0.0\",
\n \"description\": \"\",
\n \"main\": \"app.js\",
\n \"scripts\": {
\n \"start\": \"node app.js\"
\n },
\n \"keywords\": [],
\n \"author\": \"\",
\n \"license\": \"ISC\",
\n \"dependencies\": {
\n \"async\": \"^3.1.0\",
\n \"axios\": \"^0.19.0\",
\n \"bcrypt\": \"^4.0.1\",
\n \"chalk\": \"^2.4.2\",
\n \"connect-redis\": \"^4.0.4\",
\n \"cors\": \"^2.8.5\",
\n \"express\": \"^4.17.1\",
\n \"mongodb\": \"^3.2.7\",
\n \"nconf\": \"^0.10.0\",
\n \"nodemailer\": \"^6.3.0\",
\n \"pug\": \"^2.0.4\",
\n \"reading-time\": \"^1.2.0\",
\n \"redis\": \"^2.8.0\",
\n \"winston\": \"^3.2.1\"
\n }
\n}
\n<\/code><\/p>\nStep 4: File system module.<\/h2>\n
\nconst fs = require('fs');
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nfs.readFile('.\/lorem.txt', (err, data) => {
\n if(err) {
\n return console.log('Error occurred while reading file');
\n }
\n console.log(data.toString());
\n});
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nconst data = fs.readFileSync('.\/lorem.txt'); console.log(data.toString());
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nconst path = '.\/config.js';
\nfs.access(path, fs.F_OK, (err) => {
\n if (err) {
\n console.error(err);
\n return;
\n }
\n});
\n<\/code><\/p>\n\n
\nconst fs = require('fs');
\nfs.open('file.txt', 'w', (err, file) => {
\n if (err) {
\n throw err;
\n }
\n console.log('Saved!');
\n});
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nfs.writeFile('file.txt', 'Hello Word!', (err) => {
\n if (err) {
\n throw err;
\n }
\n console.log('Saved!');
\n});
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nfs.appendFile('file.txt', ' Hello World', (err) => {
\n if (err) {
\n throw err;
\n }
\n console.log('Updated!');
\n});
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nfs.unlink('file.txt', (err) => {
\n if (err) {
\n throw err;
\n }
\n console.log('File deleted!');
\n});
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nfs.rename('newfile.txt', 'oldfile.txt', (err) => {
\n if (err) {
\n throw err;
\n }
\n console.log('File Renamed!');
\n});
\n<\/code><\/p>\n
\nconst fs = require('fs');
\nfs.copyFile(file.txt', 'copyfile.txt', (err) => {
\n if (err) {
\n throw err;
\n }
\n console.log('File is copied!');
\n}); <\/p>\nStep 5: Express framework<\/h2>\n
\n
\nnpm init --y
\n<\/code><\/p>\nnpm install --save express<\/code> <\/p>\n
\nconst express = require('express');
\nconst app = express(); <\/p>\n
\n<\/code><\/p>\n\n
\nconst express = require('express');
\nconst app = express();
\nconst router = express.Router(); <\/p>\n
\n res.send('Hello World, This is home router');
\n}); <\/p>\n
\n res.send('
\n Hello World, This is profile router
\n ');
\n}); <\/p>\n
\n res.send('
\n Hello World, This is login router
\n ');
\n}); <\/p>\n
\n res.send('
\n Hello World, This is logout router
\n ');
\n}); <\/p>\n
\n<\/code><\/p>\n
\nnode app.js
\n<\/code><\/p>\n![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/express-app-start.png\")
<\/p>\n![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/express-home-routes.png\")
<\/p>\n![\"Nodejs](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/express-profile-page.png\")
<\/p>\n\n
Application middleware<\/h3>\n
\nconst express = require('express');
\nconst app = express(); <\/p>\n
\n console.log('Time:', Date.now());
\n next();
\n}); <\/p>\n
\n<\/code><\/p>\nRouter middleware<\/h3>\n
\nconst express = require('express');
\nconst app = express();
\nconst router = express.Router();<\/p>\n
\n console.log('Time:', Date.now());
\n next();
\n});<\/p>\n
\n res.send(\"ok\")
\n});<\/p>\n
\napp.listen(process.env.port || 3000);<\/p>\n
\n<\/code><\/p>\nerror-handling middleware<\/h3>\n
\napp.use((err, req, res, next) => {
\n res.status(500).send('Something broke!')
\n});
\n<\/code><\/p>\nBuilt-in middleware<\/h3>\n
Third-party middleware<\/h3>\n
npm install body-parser<\/code><\/p>\n
\nconst express = require('express');
\nconst bodyParser = require('body-parser');
\nconst app = express();
\nconst router = express.Router(); <\/p>\n
\n res.send('
\n Hello World, This is home router
\n ');
\n}); <\/p>\n
\n res.send('
\n Hello World, This is profile router
\n ');
\n}); <\/p>\n
\n res.send('
\n Hello World, This is login router
\n ');
\n}); <\/p>\n
\n res.send('
\n Hello World, This is logout router
\n ');
\n}); <\/p>\n
\napp.use(bodyParser.json()); <\/p>\n
\n<\/code> <\/p>\n
\nnpm install --save express-session
\n<\/code><\/p>\n
\napp.use(session({secret: 'some secrets'}));
\n<\/code><\/p>\nStep 6: Databases – MySQL, MongoDB, PostgreSQL and Redis.<\/h2>\n
\n
MySQL<\/h3>\n
\nnpm install --save mysql
\n<\/code><\/p>\n
\nconst mysql = require(\"mysql\");<\/p>\n
\n connectionLimit: 100,
\n host: \"localhost\",
\n user: \"root\",
\n password: \"\",
\n database: \"database_name\",
\n debug: false,
\n});<\/p>\n
\n if (err) {
\n console.log(\"error occurred during the connection.\");
\n }
\n console.log(rows[0]);
\n});
\n<\/code><\/p>\nMongoDB<\/h3>\n
![\"MongoDB](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/mongodb-connection.png\")
<\/p>\n![\"MongoDB](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/MongoDB-Find.png\")
<\/p>\n![\"Redis](\"https:\/\/codeforgeek.com\/wp-content\/uploads\/2016\/05\/Screen-Shot-2016-05-18-at-12.06.02-AM.png\")
<\/p>\n