NodeJS

Intro

Node.js is a helpful run-time environment that is able to quickly and easily run JavaScript code and this tutorial will show how to set up Node.js from with things like, installation, REPL commands, Node package manager, and setting up Node.js with MySQL for database queries.

Node.js is a server-side platform built from Google Chrome’s JavaScript Engine. Node.js is open source, cross-platform runtime environment for developing on the server-side. Node.js is written in JavaScript and can be ran on OS X, Microsoft, Windows, and Linux. [Tutorialspoint]

Node.js also provides a library with many JavaScript modules which simplifies the creation of web applications.

Node.js uses non-blocking, even-driven input/output to remain efficient in data- intensive real-time applications that runs across many devices.

History

Node.js was first created by Ryan Dahl and was developed and maintained by Dahl which later got sponsored and supported by Joyent. Dahl created Node.js because he had a distaste about the way Apache Http server used to handle a lot of concurrent connections and how the code being created was either blocked by the entire process or implied multiple execution stacks. [Thinkmobiles]

Getting started on Installing Node.js

Starting off, if you’re installing Node.js on Windows then you can just go to nodejs.org and download, follow the prompts and you’re set. A thing to take note is that the default path that it is installed at is C:\Program Files\nodejs\bin that will be the Node.js directory.

On the other hand if the user installing on UNIX/Linux/Mac OS X or SunOS they’ll first need to download and extract the archive into /temp, and move the extracted files into a specified directory directory for Node.js.

Command Code

$ cd /temp
$ wget http://nodejs.org/dist/v10.15.3/node-v10.15.3-linux-x64.tar.xz
$ tar xvfz node-v10.15.3-linux-x64.tar.xz
$ mkdir - /usr/local/nodejs
$ mv node-v10.15.3-linux-x64/* /user/local/nodejs

To make sure it’s installed and working validate it by executing a file. The user can easily do this by making a file like test.js on their machine and have some test code like following.

Test for Installation

console.log("This is a test.")

After that execute test.js on the Node.js interpreter to see the result.

Executing test

$ node test.js

If it is installed correctly it should print.

Executing test

This is a test.

Getting an Application Started

Next up to create the server you will have to call on the http module and then use that to create a server and bind it to a port.

First Application

var http = require("http");

http.createServer(function(request, response){
response.writeHead(500, {'Content-Type': 'text/plain'});
response.end('Test');
}).listen(8080);
console.log("First application instance");

Line one uses the require directive to store the returned HTTP instance into an http variable from http module. On line three is where you create an http instance by calling the http.createServer() method that creates the server instance and then on line six you bind it to port 8080. By default, once the user starts the server it’ll automatically go to http://127.0.0.1:8080 in a web browser. The result should be what you put into response.end() on line five. To stop the server instance, just hit Ctrl+c in the command line.

Node.js Virtual Environment

Node.js comes with a virtual environment called REPL (also Node shell). REPL is the abbreviation of Read-Eval-Print-Loop. Its a way to quickly test simple Node.js/JavaScript code.

To start up REPL is as easy as just typing node into the command console. After typing node and hitting enter, the user will able to run JavaScript, use variables and multiline expressions.

REPL Commands

Command	Action
ctrl+c	Terminates current command
ctrl+c twice	Terminate the Node REPL
ctrl+d	Terminate Node REPL
up & down keys	See command history and modify previous commands
tab Keys	List of current commands
.help	List all commands
.break	Exit from multiline expression
.clear	Exit multiline expression
.save “filename”	Save current Node REPL session
.load “filename”	Load file content into current Node REPL session

Note

As an add on to get the last result, “_” can be used to get that.

Node Package Manager (NPM)

NPM has two main functionalities: online repositories for node.js packages and modules, and command line utility to install Node.js packages, and do version management and dependency management.

To check the current version of NPM just do the type the following in the command console-

Checking Version

npm --version

If it is an old version of NPM the user can update using the following command-

Update NPM Version

$ sudo npm install npm -g
/usr/bin/npm -> /usr/lib/node_modules/npm/bin/npm-cli.js
npm@6.4.1 /usr/lib/node_modules/npm

Code used from [Tutorialspoint]

Installing Modules

Next up to install a module and use it in a JavaScript file, in the command line type-

Install prompt

npm install <Module Name>

Next go to JavaScript and type in the following-

Using the Module

var variableName = require('/path/to/file')

In the code above we use the require function which is a module in Node that is on a global scope so it’s always available. The require is the command that calls on the modules where they’re located locally. [Buna]

By default NPMs installs any dependency in the local mode. Where the local mode refers to the package installation in node_modles directory in the folder where Node is present. To globally install a module use-

npm install "modulename" -g

This will store the packages and dependencies in system directory and cannot be imported using require() in the Node application directly.

Note

To check all modules installed us npm ls and npm ls -g to check globally installed packages.

Uninstalling, Updating, Searching a Module

Uninstalling, updating and searching a module is simple and can easily be done by doing the following -

Update, uninstall, search

$ npm uninstall "ModuleName"

$ npm update "ModuleName"

$ npm search "ModuleName"

Package.json

package.json is in the root directory of any Node application/module and is used to define properties of a package.

Attributes of Package.json

• Name - name of the package
• Version - version of the package
• Description - Description of the package
• Homepage - Homepage of the package
• Author - Author of the package
• Contributors - Name of contributors to the package
• Dependencies - List of dependencies
• Repository - Repository type and URL of the package
• Main - Entry point of the package
• Keywords - Keywords

Creating Modules

Now that the basics are done, the user can also create a module. This requires package.json to be generated. Using NPM will generate a basic skeleton of package.json.

Create modules

$ npm init

npm help json
npm install <pkg> --save
^C
Name:(webmaster)

After $ npm init is used, the command prompt will walk the user through making a package.json file that covers common items. For help for package.json documentation, $ npm help json will show definitive documentation on the package.json fields and what they do. $ npm install <pkg> --save will install the package and save it as a dependency in package.json file.

Next up is registering the user with the NPM repository site using a valid email address. This can be done by doing the following-

Publishing modules

$ npm adduser
Username: "Your username"
Password: "Your password"
Email: "Your email"
$ npm publish

npm publish is when the user actually publishes the modules, but before that a valid account is needed. An important thing to note is that the email address will be public and on the internet and in the fields where it says “Your …” put in the respective username, password, and email for the user that is publishing the module.

Setting up Node.js with MySQL

There are many ways to set up Node.js with a database and it may seem complicated, but it’s actually simple and this quick tutorial will show how to connect Node.js with MySQL.

First up, how to install the MySQL module. This can be done in the command console. After the module is installed, the next step is to make a JavaScript file that creates the connection and what will be used to query the database.

Installing MySQL module

npm install mysql

Connecting to a database

var mysql = require('mysql')

var con = mysql.createConnection({
    host: "localhost"
    user: "yourUserName"
    password: "yourPassword"
    });

    con.connect(function(err){
    if (err) throw err;
    console.log("Connected")

    con.query(sql, function (err, result){
    if(err) throw err;
    console.log("Result: " + result)
    })
})

[W3Schools] used as reference code

Where the user made the variable con is where the user will create a connection, and this means you’ll have to enter the correct information about the database, such as the host, user, and password. After that the function after will make the connection and handle any errors. With con.query() how the user makes the statement they want is to replace is by replacing the part of the code where it says sql in the con.query() function. The whole sql statement will have to go before the function is called.

Conclusion

In conclusion, Node.js is a helpful tool for quick testing of a javascript file that can be helpful and reliable. The best thing about Node.js is the amount of modules a user can get to help the person do what they need.

Sources

[Buna]

Samer Buna “Requiring modules in Node.js: Everything you need to know” Freecodecamp, Web. 19 Mar, 2017

[Thinkmobiles]

“Why use Node.js - look behind the scenes of web development” Thinkmobiles, Web. 04 Apr, 2019

[Tutorialspoint]

(1, 2) “Node.js Tutorial” Tutorialspoint, Web. 02 Apr. 2019

[W3Schools]

“Node.js MySQL” W3Schools, Web. 18 Apr. 2019