Overview of Node JS

JACOB NELSON
SOFTWARE ARCHITECT

Node.js is not a silver-bullet new platform that will
dominate the web development world. Instead,
it’s a platform that fills a particular need.

A word of warning
There are some really excellent JavaScript people out
there. I'm not one of them.

Node JS is a powerful tool for controlling web
servers, building applications, and creating event-
driven programming and it brings JavaScript, a
language familiar to all web developers, into an
environment independent of web browsers.

Node.js® is a JavaScript runtime built
on Chrome'sV8 JavaScript engine.

Runtime is when a program is
running (or being executable).That is,
when you start a program running in
a computer, it is runtime for that
program.

Node.js is not a JavaScript framework

Node.js allows you to run JavaScript
code in the backend, outside a
browser.

Node.js ships with a lot of useful
modules, so you don't have to write
everything from scratch

Thus, Node.js is really two things:
a runtime environment and a library.

Requirements
▪ JavaScript
▪ Command-LineTool

V8
TheV8 JavaScript Engine is an open source JavaScript
engine developed byThe Chromium Project for the
Google Chrome web browser. It has seen used in
many other projects, such as Couchbase, MongoDB
and Node.js.
https://en.wikipedia.org/wiki/V8_(JavaScript_engine)

Threading
Node is single-threaded and uses a concurrency
model based on an event loop. It is non-blocking, so it
doesn't make the program wait, but instead it
registers a callback and lets the program continue.
This means it can handle concurrent operations
without multiple threads of execution, so it can scale
pretty well.

Installing Node
If you're using OS X orWindows, the best way to
install Node.js is to use one of the installers from the
Node.js download page.
If you're using Linux, you can use the installer, or you
can check Node Source's binary distributions to see
whether or not there's a more recent version that
works with your system.

npm, the official Node package manager
npm is the package manager for JavaScript.
npm makes it easy for JavaScript developers to share
and reuse code, and it makes it easy to update the
code that you're sharing.

Node comes with npm installed so you should have a
version of npm. However, npm gets updated more
frequently than Node does, so you'll want to make
sure it's the latest version.

▪ It installs application dependencies locally, not globally.
▪ It handles multiple versions of the same module at the
same time.
▪ You can specify tarballs or git repositories as
dependencies.
▪ It's really easy to publish your own module to the npm
registry.
▪ It's useful for creating CLI utilities that others can install
(with npm) and use right away.

Npm behind firewall
npm config set proxy http://gateway.zscaler.net:9400
npm config set https-proxy
http://gateway.zscaler.net:9400

Updating npm
npm install npm@latest -g

Your First Program
console.log('HelloWorld');

npm init
The npm init command is a step-by-step tool to scaffold
out your project. It will prompt you for input for a few
aspects of the project in the following order:

npm init
▪ The project's name
▪ The project's initial version
▪ The project's description
▪ The project's entry point (meaning the project's main file)
▪ The project's test command (to trigger testing with something like Standard)
▪ The project's git repository (where the project source can be found)
▪ The project's keywords (basically, tags related to the project)
▪ The project's license (this defaults to ISC - most open-source Node.js projects are
MIT)

npm init
Once you run through the npm init steps above, a
package.json file will be generated and placed in the
current directory. If you run it in a directory that's not
exclusively for your project, don't worry! Generating a
package.json doesn't really do anything, other than create
a package.json file.You can either move the package.json
file to a directory that's dedicated to your project, or you
can create an entirely new one in such a directory.

npm init options
If you invoke it with -f, --force, -y, or --yes, it will use only
defaults and not prompt you for any options.

package.json
package.json file can be described as a manifest of your
project that includes the packages and applications it
depends on, information about its unique source control,
and specific metadata like the project's name, description,
and author.

package.json
package.json also contains a collection of any given project's
dependencies.These dependencies are the modules that the project
relies on to function properly.

package.json - dependencies
Dependencies are specified in a simple object that maps a package
name to a version range.The version range is a string which has one or
more space-separated descriptors.
Having dependencies in your project's package.json allows the project
to install the versions of the modules it depends on. By running an
install command inside of a project, you can install all of the
dependencies that are listed in the project's package.json - meaning
they don't have to be (and almost never should be) bundled with the
project itself.

package.json - devDependencies
It also allows the separation of dependencies that are needed for
production and dependencies that are needed for development. In
production, you're likely not going to need a tool to watch yourCSS
files for changes and refresh the app when they change.

package.json – module version
▪ version Must match version exactly
▪ >version Must be greater than version
▪ >=version etc
▪ <version
▪ <=version~version "Approximately equivalent to version"
▪ ^version "Compatible with version"
▪ 1.2.x 1.2.0, 1.2.1, etc., but not 1.3.0

package.json – module version
▪ http://...
▪ * Matches any version
▪ "" (just an empty string) Same as *
▪ version1 - version2 Same as >=version1 <=version2.
▪ range1 || range2 Passes if either range1 or range2 are satisfied.
▪ git...
▪ user/repo See 'GitHub URLs' below
▪ tagA specific version tagged and published as tag
▪ path/path/path

Modules - Installation
npm install <-g> module name

Modules – Installation
npm install
Once you run this, npm will begin the installation process of all of the
current project's dependencies.

Modules – Installation Options
npm install <module> --save
when installing a module: --save, it will install and save it as an entry in
the dependencies
npm install <module> --save-dev
when installing a module: --save-dev, it will install and save it as an
entry in the devDependencies

Modules – Listing
Sometimes is useful to see the list of packages that you have installed
on your system.You can do that with the following commands:
# list all installed modules with dependencies
npm ls
# list all installed modules without dependencies
npm ls --depth=0
# list all installed globally dependencies
npm ls -g --depth=0

Extraneous Modules
Modules which are installed and are found on node_modules folder, but
not included as Dependency or devDependency in package.json

Module – uninstallation
# uninstall package and leave it listed as dep
npm uninstall <package_name>
# uninstall and remove from dependencies
npm uninstall --save <package_name>
# uninstall global package
npm uninstall -g <package_name>
# remove uninstalled packages from node_modules
npm prune

Modules – view all versions of an NPM
Package
The easy way to view all released versions of an npm package is to use
the following command
npm show <module>@* version

Modules - Importing
▪ Java or Python use the import function to load other libraries,
▪ PHP and Ruby use require.
▪ In Node you can load other dependencies using the require keyword.

Modules - Importing
▪ For example, we can require some core modules:
▪ var http = require('http');
▪ var dns = require('dns');

Modules - Importing
What node.js will do in this case, is to first look if there is a core module
named http, and since that's the case, return that directly. But what
about non-core modules, such as 'mysql'?
In this case node.js will walk up the directory tree, moving through each
parent directory in turn, checking in each to see if there is a folder
called 'node_modules'. If such a folder is found, node.js will look into
this folder for a file called 'mysql.js'. If no matching file is found and the
directory root '/' is reached, node.js will give up and throw an exception.

Modules - Importing
▪ We can also require relative files:
▪ var myFile = require('./myFile'); // loads myFile.js

callbacks
In asynchronous programming we do not return values when our
functions are done, but instead we use the continuation-passing style
(CPS).
With this style, an asynchronous function invokes a callback (a function
usually passed as the last argument) to continue the program once the
it has finished.

When Not to Use?
▪ CPU heavy apps
▪ Simple CRUD / HTML apps
▪ NoSQL + Node.js

When to Use?
▪ JSON APIs
▪ Single page apps
▪ Streaming Data
▪ Soft Real time Applications

▪ https://www.guru99.com/node-js-tutorial.html
▪ http://www.tutorialsteacher.com/nodejs/nodejs-basics
▪ https://www.javatpoint.com/what-is-nodejs
▪ http://adrianmejia.com/blog/2016/08/19/Node-Package-Manager-NPM-
Tutorial/
▪ https://nodesource.com/blog/an-absolute-beginners-guide-to-using-npm/
▪ Best Practices
▪ https://www.codementor.io/mattgoldspink/nodejs-best-practices-
du1086jja

Overview of Node JS

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