Tag: nodejs

Node.js is an open source, cross-platform, server-side environment for building fast, scalable network applications. The applications of Node.j are written in JavaScript and run by Google's V8 JS engine. You can use it to effectively execute JavaScript code on the server. Here are some key features:

• Totally asynchronous: All calls in Node.js are asynchronous and therefore do not block execution. This is accomplished with Events and Promises, patterns that occur in the JavaScript language.
• Single Threaded: Node.js works on a single thread only, which works well with its event-driven architecture. Node.js applications are fast and scalable because they never buffer data.
• Free licensed: Node.js is released under the MIT license, so you can do almost anything with the source code.

If you need CPU-intensive calculations, Node.js may not be the right choice for you. It is severely limited by using only one thread, and you should probably use C ++ or Python instead. What kind of apps is Node.js suitable for?

• Web applications
• I / O-bound apps
• API services

The list of companies that use it speaks volumes about its usefulness: PayPal, Netflix, Ebay, Walmart, Medium.com, Mozilla, NASA, Linkedin, Trello … You can also find thousands of individual projects in Node.js.

What will we cover?

• Install the latest Node.js,
• What is REPL and how is it used?
• What are NPM packages and how can they be used?
• Create a sample web app in Node.js

requirements

• A clean VPS with root access,
• runs Ubuntu 16.04
• At least 512 MB of RAM, 1 GHz CPU and 20 Gb of hard disk space.
• Understanding JavaScript.

Step 1: Install the latest Node.js

First log in to your VPS as root about SSH. Navigate to the / tmp directory by running the following command:

cd / tmp

Install curl:

fittingly install curl -y

Download the install script for the latest NodeJS version:

curl -sLO https://deb.nodesource.com/setup_12.x

At the time of writing this article, the latest version of Node.js was version 12. New versions will be released in April and October. Replace the new version number in the above command to install a newer version.

Run it with:

bash setup_12.x

The script sets up the right Ubuntu package repositories. It will take a while to run. When the process is complete, install Node JS and the compilation tools by doing the following:

apt install -y nodejs gcc g ++ make

You also have gcc, g ++ and make installed. It may be required by some Node.js packages during installation to compile their parts written in C or C ++. Learn more about Node.js packages later in the tutorial.

After the installation completes, run the following command to verify the version of Node.js:

nodejs -v

If a version is displayed (which was v12.2.0 at the time of writing), you have installed Node.js correctly. If an error is displayed, check the entered commands against those shown above.

Step 2: Information about Node.js REPL

REPL stands for Read-Eval-Process-Loop and is an interactive environment for Node.js. You execute a single expression and the result is immediately printed back. It's a great way to experiment with the language.

Run the built-in Node.js REPL file with the following command:

NodeJS

The following is displayed:

Welcome to Node.js v12.2.0.
Enter ".help" for more information.
>

The REPL now waits for you to enter an expression. Try simple calculations by typing:

1 + 2

The result is 3. Brackets are also noted:

(1 + 2) * 5

You can now try to perform some of Node's built-in functions, such as: For example, printing on the console:

console.log (& # 39; Hello! & # 39;)

The issue will be:

Hello!
not defined

The REPL executed the call console.log (), which says "hello!" not defined(gray in the next line) means that the call has not returned anything.

Variables are also supported:

a = 5
b = 6

You can try adding them:

a + b

The result is 11 in yellow, which denotes a number. (Green denotes a string.)

You can use the up and down arrows to navigate the command history. To list all available commands, press the Tab key twice.

Press CTRL + C twice to exit Node.js REPL.

Step 3: Information about NPM packages

NPM (Node Package Manager) is the world's largest JavaScript library registry with package manager capabilities. Both open source developers and large companies use it to simplify software development. NPM can be used for free and is included in Node.js since version 0.6.3.

The biggest advantage of NPM is the package manager. You specify all your project dependencies in a file named package.json. All you have to do to start development is execution npm install, It is also possible to specify specific versions of packages that your project works with.

Make sure npm is installed and verify the version by doing the following:

npm -v

Local and global package installations

With NPM, installing packages is easy. To install a package locally, just do the following:

npm install 

and NPM takes care of all dependencies for you. When you install a package locally, the files are downloaded from NPM and stored in a directory named nodemodules_ in the current directory.

For example, if you want to install locally Cheerio (a server-side optimized version of jQuery) you must do the following:

npm install cheerio

When cheerio finishes the installation, you can import it from your code with this line:

const cheerio = require (& # 39; cheerio & # 39;);

The Cheerio Object provides access to the functionality of the library.

If you & # 39; -g & # 39; Passed to npm install, you can install packages globally. You can access them through the CLI, but you can not import them from the code. To list all globally installed packages, do the following:

npm ls -g

Update, Uninstall, Search

To update a package, use npm update:

npm update 

To uninstall a package, use npm uninstall:

uninstall npm 

You can also search for a package by name using npm search:

Npm search 

You will receive a tabular list of packages whose name matches the one you have submitted.

Create a new package

file package.json stores information about the package. Creating a package.json is only useful if you want to publish your library in the npm package registry.

In the working directory of your package, run the following command to create one interactively:

npm init

You will be asked for your package name, the current version, the description, the entry point file, the test run command, the git repository, the keywords, your author's name, and the code license. NPM then asks you if you are satisfied with the generated JSON. If so, type "y" or press Enter.

NPM then saves the newly generated package.json in the current directory.

Publish a package

To publish a package in the NPM package registry, you must first set up an account at npmjs.org.

If you are not already logged in, you must log in to NPM before you publish a package. You can add a new user to npm with the following command:

npm adduser

NPM will ask for your user name, password and e-mail address (which will be displayed publicly). When you're done, you can publish your package by running the following command from the working directory of your package:

publish npm

Step 4: Create a sample web server app

We're now creating a simple web server app that returns the requested URL in uppercase. To create an HTTP server, we use the built-in http To convert characters to uppercase, we use the command uppercase Package from NPM. Install the latter with this command:

npm install capital letters

Navigate to the home directory:

cd ~

Open a file named Uppercase http.js for processing:

Nano-uppercase-http.js

Add the following lines:

var http = require (& # 39; http & # 39;);
var uc = require (capital letters);
console.log (& # 39; starting ... & # 39;);
http.createServer (function (req, res) {
console.log (& # 39; received request for URL: & # 39; req.url);
res.writeHead (200, {& # 39; Content-Type & # 39 ;: & # 39; text / html & # 39;});
res.write (uc (req.url + & # 39; n & # 39;));
send again();
}). listen (8080);

Save and close the file.

First we will need two packets (http and uppercase) and save them in separate variables (http and uc, respectively). Then we call that create server Http package method and pass it a function that will be executed when the server receives a request; The request itself is stored in variable req,

The function writes the content type Heading of the type text / html to the response variable resand tells the customer that the answer is in HTML. In the line beginning with res.write () we call uc (the package in uppercase), which returns the capital letter variant of the requested URL and appends a new line.

The last two lines end the answer with a call The End() and instruct the HTTP server to listen on port 8080. You can specify any other port, if it is free when running the app.

Run the app:

Node uppercase-http.js

You will see the following message:

starting ...

Start another terminal for testing and connect to your VPS root about SSH and curl localhost: 8080:

Curls localhost: 8080

The output is a slash (/) because you did not request a more specific path. Try curls / hello:

Curls localhost: 8080 / hello

You get the following answer:

/HELLO

The program has correctly converted the path to uppercase letters. If you look at the server app itself, a status message was displayed for both requests:

Received request for URL: /
Request for URL received: / Hello

If you want to access this app through your web browser, you must configure a reverse proxy (probably with nginx) that is not included in this tutorial.

Conclusion

Now that you know how to install Node.js and use NPM, you can create hobby projects over the weekend or try to create the next Netflix! Node.js is flexible enough to run on the cheapest servers, and you can continue to create a professional web app.

Dusko Savic is a technical writer and flutter programmer.

DuskoSavic.com