About This Project

NodeJS - Express, Mongo, Sequelize, Mongoose, Socket.io, REST APIs, ReactJS Social Network & lot more. My personal notes and apps.

Author

Aditya Hajare (Linkedin).

Current Status

WIP (Work In Progress)!

Deployed On Heroku

• Weather App: https://aditya-hajare-weather-app.herokuapp.com
• Tasks Manager App: https://aditya-hajare-nodejs-task-app.herokuapp.com
• Socket.io Chat App: https://aditya-hajare-socket-chat-app.herokuapp.com

License

Open-sourced software licensed under the MIT license.

---

Important Notes

• Debugging Using Node Debugger
• Call Stack
• Event Loop
• Deploying Weather App On Heroku
• JEST - Things To Know
• WebSockets Protocol
• Mongoose - Things To Know
• Cookies
• Sessions
• Storing Sessions In MongoDB
• Allow CORS For REST APIs

Debugging Using Node Debugger

• Add debugger keyword wherever you want to stop your program execution and begin debugging. For e.g.:

  //app.js
  
  console.log('Hello World');
  debugger; // This is where program execution will stop and you can start debugging.
  console.log('Hello World 1');
  

• Run app.js above with inspect command as below:

  // In terminal
  
  node inspect app.js
  

• Open Google Chrome Browser and enter following URL:

  chrome://inspect/#devices
  

• You should see your current Node app under Remote Target. Click on inspect link.
• On left hand side, click on Add folder to workspace.

Call Stack

• Call Stack is a simple data structure provided by the V8 JavaScript Engine.
• It's job is to track the execution of our program and it does that by keeping track of all of the functions that are currently running.
• The Call Stack data structure uses FILO (First In Last Out) to track the execution of our program.

Event Loop

• Event Loop looks at 2 things:
  • It looks at the Call Stack.
  • And it looks at the Callback Queue.
• If the Call Stack is empty, it's going the run the items from Callback Queue.
• The Event Loop actually have to wait until Call Stack is empty before it could run items from Callback Queue.
• None of our Asynchronous Functions are going to run unless main() Function is done executing.
• Node uses other threads (C++) behind the scene for Node APIs.

Deploying Weather App On Heroku

• Go to local Git repository root directory or project root directory.
• Execute following command:

  heroku create [SUB_DOMAIN]
  
  // For e.g.
  heroku create aditya-hajare-weather-app
  

• NOTE: aditya-hajare-weather-app is the sub-domain and it must be unique across Heroku.
• From your project root, execute following command:

  heroku git:remote -a [APP_NAME]
  
  // For e.g.
  heroku git:remote -a aditya-hajare-weather-app
  

• Execute git remote to list remote branches. You should see something like below:

  heroku
  origin
  

• NOTE: heroku is listed under remotes.
• To Deploy:
  • To deploy master branch to Heroku:

  git push heroku master
  

  • To deploy contents of specific directory to Heroku root:

  git subtree push --prefix [DIRECTORY_NAME] heroku master
  
  // For e.g.
  git subtree push --prefix 10-Weather-App-Express heroku master
  

• After deployment, you can visit your app in browser. For e.g.

  // Weather App on Heroku:
  https://aditya-hajare-weather-app.herokuapp.com/
  

• Heroku Environment Variables:
  • To set environment variable in Heroku environment:

    heroku config:set KEY=VALUE
    

  • To unset/remove environment variable in Heroku environment:

    heroku config:unset KEY
    

JEST - Things To Know

• .toBe() uses === operator to compare values. i.e.
  • 1 === 1: True
  • {} === {}: False. That is because when 2 objects are compared with === they are not equal as they are stored in different memory locations.
• To compare objects in JEST, use .toEqual().

WebSockets Protocol

• WebSocket is a separate protocol from HTTP.
• WebSockets allow for Full Duplex Communication.
• Full Duplex Communication is just a fancy term for Bi-Directional Communication.
• With WebSockets we have a Persistent Connection between client and server.
• Socket.io needs to be called with a raw HTTP Server.
• Event emitters:
  • socket.emit('EVENT_NAME', { dataObject }): Only to self/specific client.
  • socket.broadcast.emit('EVENT_NAME', { dataObject }): All other clients except self.
  • io.emit('EVENT_NAME', { dataObject }): All clients including self.
• Event emitters in Rooms:
  • io.to(room).emit('EVENT_NAME', { dataObject }): Emits an events to everybody in a specific room.
  • socket.broadcast.to(room).emit('EVENT_NAME', { dataObject }): Emits an events to everybody in a specific room except self/specific client.

Mongoose - Things To Know

• While defining methods on Schema, avoid Arrow Functions. Instead opt out for function().
  • **Reason: ** this is not available in Arrow Functions.
  • Refer to following examples:

  17-Shop-App-Mongoose/models/user.js
  11-Tasks-Manager-App/src/models/user.js
  11-Tasks-Manager-App/src/models/task.js
  

  • For e.g.

  const mongoose = require('mongoose');
  
  const userSchema = mongoose.Schema({
      name: {
          type: String,
          required: true
      },
      email: {
          type: String,
          required: true
      }
  });
  
  userSchema.methods.helloWorld = function() { // Not using arrow function here!
      // Code
  };
  
  module.exports = mongoose.model('User', userSchema);
  

Cookies

• Cookies which are not having expiry and max-age set, will get destroyed when browser is closed.
• To set a cookie:

exports.postLogin = async (req, res, next) => {
    res.setHeader('Set-Cookie', 'isAuthenticated=true; HttpOnly');
    res.send(req.body);
}

• To fetch value of isAuthenticated cookie:

const value = req.get('Cookie')
    .split(';')[1]
    .trim()
    .split('=')[1];

Sessions

• To use sessions in Express, install following plugin:

npm i express-session --save

• Steps to initialize and use session:
  • Initilize session in middleware in app.js:

  const session = require('session');
  
  const app = express();
  
  app.use(session({
      secret: 'some secret string',
      resave: false,
      saveUninitialized: false
  }));
  

  • Session will be available on req.session.
  • To set a value in session:

  req.session.isLoggedIn = true;
  

  • To fetch a value from session:

  const loggedIn = req.session.isLoggedIn;
  

Storing Sessions In MongoDB

• Install following package:

npm i connect-mongodb-session --save

• Setup MongoDB Store:

const session = require('session');
const connectMongoDBSession = require('connect-mongodb-session');

const MongoDBStore = connectMongoDBSession(session);
const store = new MongoDBStore();

app.use(session({
    secret: 'some secret string',
    resave: false,
    saveUninitialized: false,
    store
}));

Allow CORS For REST APIs

• Method #1:
  • Using express cors middleware package:
    • Install cors npm package:

    npm i cors --save
    

    • Use it in app.js:

    const express = require('express');
    const cors = require('cors'); // CORS
    const bodyParser = require('body-parser');
    
    const app = express();
    
    app.use(bodyParser.json());
    app.use(cors()); // CORS
    
    app.listen(8080);
    

• Method #2:
  • Manually setting headers (NOTE: May not work in most cases):

  const express = require('express');
  const bodyParser = require('body-parser');
  
  const app = express();
  
  app.use(bodyParser.json());
  app.use((req, res, next) => {
      // CORS Middleware
      res.setHeader('Access-Control-Allow-Origin', '*');
      res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, PATCH, DELETE');
      res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');
      next();
  })
  
  app.listen(8080);