nodejs.txt

* Node.js is an open-source, cross-platform JavaScript run-time environment that executes JavaScript code outside of a browser.
* NodeJs is a C++ program that includes Google's V8 engine.
* Express.js, or simply Express, is a web application framework for Node.js


Commannds:
----------------------------------
* npm init (OR) npm init --yes (OR) npm init -y
* npm list = to see all the dependency packages
* npm install underscore (OR) npm i underscore
* npm i -g lodash = It install "lodash" package globally
* npm root -g = it gives the path that where all the global packages are instaling
* npm i -g npm@5.0.1 = This is how we can install a package with particular version
* npm uninstall -g npm (OR) npm un -g npm (OR) npm remove -g npm (OR) npm rm -g npm = It removes globally
* npm uninstall underscore (OR) npm un underscore (OR) npm remove underscore (OR) npm rm underscore
* npm i mocha --save-dev (OR) npm i -D mocha
* npm list (OR) npm ls = To get all the modules with version number that are installed.
* npm list --depth=0 (OR) npm ls --depth=0 (OR) npm ls --depth 0 = To get only the modules with version number that are installed by us.
* npm view mongoose = To view package.json file a particular module
* npm view mongoose dependencies
* npm view mongoose versions
* npm outdated
* npm update mongoose@
* npm i -g npm-check-updates

* npm config get init-author-name = It gives the default author name
* npm config set init-author-name "Manoj" = It sets the default author name to "Manoj"
* npm config delete init-author-name = It deletes the previously set author name to default


* npm cache clean --force

-----------------------------------

Semantic versioning (SemVer) example = 5.0.1
5 = Major
0 = Minor
1 = Patch release

^5.0.1 = 5.X
~5.0.1 = 5.0.X

* Every node module contains package.json file


Few ExpressJS middlewares
--------------------------------------
helmet = Secures our app by setting variour HTTP headers
app.use(helmet());

morgan = logs all the HTTP requests -> It impacts the request process pipeline
app.use(morgan('tiny'));
----------------------------------------


* Function expressions
* Module & Require()
* Read, Write & delete files
* Create, remove directories
* Protocols: A set of communication rules , that two sides agree to use when communicating.
* HTTP is used for websites whereas FTP is used for transfer files.
* A programme running on a computer can listen for requests sent to a particular port.
* Client & Server topics
* Streams & Buffers
* Basic routing using NodeJS
* NPM concept


* 'Ryan Dahl' embeded Google's V8 engine into C++ and named it as 'Node'
* Node is a run time javascript environment. It contains javascript engine that executes javascript code.
* Every file in Node is considered as Module.
* Variables and functions that are declared in a file are scoped to that module.
* If we want to use a variable or a function which is defined in a module from outside of that module we need to export and then import that module.
* Every Node application has at least one file/module which is called "Main Module".
* The type of the HTTP request determines the kind of the operation.
* 



********************************************************************************************
Creating server with pure NodeJS and serving files with headers:
--------------------------------------------------------------------
const http = require('http');
const path = require('path');
const fs = require('fs');

const server = http.createServer((req, res) => {
  if (req.url === '/') {
    fs.readFile(
      path.join(__dirname, 'public', 'index.html'),
      (err, content) => {
        if (err) throw err;
        res.writeHead(200, { 'Content-Type': 'text/html' });
        res.end(content);
      }
    );
  }

  if (req.url === '/api/users') {
    const users = [
      { name: 'Bob Smith', age: 40 },
      { name: 'John Doe', age: 30 }
    ];
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify(users));
  }
********************************************************************************************



Payment Gateway:
--------------------------------------------------------------------------------------------
* https://www.youtube.com/watch?v=mI_-1tbIXQI
* https://www.youtube.com/watch?v=PsvxhUAw26o
* https://www.youtube.com/watch?v=QT3_zT97_1g





NodeJS core modules:
--------------------------------------------------------------------
HTTP, path, fs, os, events, buffer, crypto

-> FS functions
    -> fs.watch(filePath, () => {});
    -> fs.readFile(filePath, (err, data) => {});
    -> fs.readFileSync(filePath);


* https://thebittheories.com/nodejs-interview-questions-935498510d46
* http://www.tutorialspoint.com/nodejs/nodejs_interview_questions.htm
* https://www.youtube.com/watch?v=-PuMp5tQ8Jw&list=PL4cUxeGkcC9jdm7QX143aMLAqyM-jTZ2x&index=15




****************************************** IMP points ************************************************
* JWT contains 3 parts
  -> Header - Algorithm token type
  -> Payload - It contains the data that we store/sent
  -> Signature

* 'middleware' is just a function that has access to the request & response cycle.






****************************************** Status codes ************************************************
* 401 = Un-Authorized
* 400 = Bad request
* 500 = Internal server error
* 404 = Not found
* 408 = Request timeout
* 






************************************** Askable Intervirew Q's ******************************************
* What's Node JS?
* Explain 'Status codes'?
* Write sample express server connection with MongoDB connetion?
* What is a 'middleware'?
* How do you protect the routes?
* 






************************************** Mongoose functions ******************************************
* findById(id);
* findOne({ email });
* findById(id).sort({date: -1});