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Node.js

  • This is document is based on a Node.js crash course.
  • Node.js is a Javascript runtime (not a language or framework) built on V8 Javascript engine written in C++.
  • Node.js allows Javascript to be used as a server side language thus the language used server-side and client-side can be the same. (No need for a python,PHP webserver backend etc. all using Javascript).
  • Node is not suitable for application that requires CPU intensive calculations.
  • Key feature of Node.js is it's non-blocking I/O model.

Non-blocking I/O operations allow a single process to serve multiple requests at the same time. Instead of the process being blocked and waiting for I/O operations to complete, the I/O operations are delegated to the system, so that the process can execute the next piece of code.

  • Non-blocking I/O can be seen as a workaround for Javascripts inability to do multi-threading. Hence Node.js relies alot on async and non blocking I/O to support concurrent connections.
  • More Sync vs Async in javascript.

Node's Event Loop

  • Below is a diagram of a Node.js thread. As can be seen below, EventEmitters fires off multiple events (processes) but the events are queued and handled in a single thread in a loop.

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NPM (Node Package Manager)

  • Used to install 3rd party packages
  • Packages are stored in "node_modules" folder
  • Dependencies for projects are listed in "package.json" file
# To generate a package.json file
npm init

# To install packages locally 
npm install <package name>

# To install packages globally (on system)
npm install -g <package name>

# To install dev dependecies in project
npm install --save-dev <package name>
npm install -D <package name>

# To install dependencies that is used by a project
npm install

Package.json

  • A file created by npm init, where all the dependencies for the project are listed in.
  • Dependencies are automatically updated in Package.json file.
  • There are 2 types of dependencies : dependencies and devDependencies.
  • devDependencies are dependencies used only for development.
  • package-lock.json is created when npm installs a dependency and it tracks all the dependencies and its versions.

Script Function

  • Below is an example of a Package.json file and within the red box is the script function.

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  • The script function allow us to use npm to run scripts enclosed within the script object denoted by their identifiers. 
# Syntax 
npm run <identifier>

# Example
npm run dev
npm run start

Node Modules

  • Something like libraries in other programming languages.
  • 3 types of modules include : Core Mods, 3rd Party Mods installed or Custom Mods
  • Node uses CommonJS, ~~only ES6 method of declaring modules is not applicable.~~ (As of current version of node ES6 method of module declaration is possible. However, we will face with #set type module in the package json error. 
    # how to declare
const module = require('path_to_module')

set "type": "module" in the package.json error

  • To resolve this error we simply need to add "type":"module" into package.json as the error states an example of where to add it can be seen below.
{
  "name": "learning_ES6",
  "version": "1.0.0",
  "description": "",
  "main": "app.js",
  **"type":"module"**,
  "author": "tinydev",
  "license": "ISC",
}

Sample Project

  • Objective : With the modules introduced below, create a Webserver that serves various web pages and content (index, about, images and 404).

Installing on Debian/Ubuntu

  • We can install Node and NPM on Debian/Ubuntu using apt package manager.
sudo apt install nodejs npm

Starting a Node Project in VS Code

# Create a new VS Code Project File
mkdir <dir_name>
cd <dir_name> && code <dir_name>
ctrl + shift + `

# Create a new node project (In VSCode Terminal)
npm init

Basic Components

Running a js file with node.

node <js_file>
nodemon <js_file>

Core Mod :

Dev Mod :

  • nodemon : a tool that helps develop Node.js based applications by automatically restarting the node application when file changes in the directory are detected.