{back-end}

the part of a computer system or application that is not directly accessed by the user, typically responsible for storing and manipulating data.

1

www.google.com

2

4

3

Method

URL

Protocol

Method

URL

Protocol

Body

{node.js}

an open-source, cross-platform, back-end JavaScript runtime environment that runs on the V8 engine and executes JavaScript code outside a web browser. 

What is Node.js?

  • Node.js is an open source server environment

1.

2.

Node.js is free

3.

Node.js runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)

# node.js

4.


Node.js uses JavaScript on the server

 

What Can Node.js Do?

  • Node.js can generate dynamic page content

1.

2.

Node.js can create, open, read, write, delete, and close files on the server

3.

Node.js can collect form data

# node.js

4.

Node.js can add, delete, modify data in your database

var http = require('http');

http.createServer(function (req, res) {
  res.write('Hello Backend Node Server!');
  res.end();
}).listen(8080);
# server

Basic NodeJs server

Make a file named "myfirst.js" with above code
open cmd with Ctrl + `
run node myfirst.js
visit localhost:8080 from your browser

var http = require('http');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write('Hello Backend Node Server!');
  res.end();
}).listen(8080);
# server

Basic NodeJs server

200 ?? - Status code, maybe you have seen 404-Not Found or 500-Internal Server Error
Content-Type ?? - This gets sent via the header, and tells the client (person who sent the request) what format the data is in

8080 ?? - Port number (default port 80)

Consider modules to be the same as JavaScript libraries.

A set of functions you want to include in your application.

What is a Module in Node.js?

Hospital == App

var http = require('http');
# modules

Include Modules

To include a module, use the require() function with the name of the module.
Node.js has a set of built-in modules which you can use without any further installation. https://www.w3schools.com/nodejs/ref_modules.asp

exports.myDateTime = function () {
  return Date();
};
# modules

Create Modules

You can create your own modules, and easily include them in your applications.

The following example creates a module that returns a date and time object:

 

Use the exports keyword to make properties and methods available outside the module file.

Save the code above in a file called "myfirstmodule.js"

Include & Use Your Own Module

var http = require('http');
var dt = require('./myfirstmodule');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write("The date and time are currently: " + dt.myDateTime());
  res.end();
}).listen(8080);
# modules

The benefits of modules is that you can code once and use it everywhere. When you need to change how the module works, you just need to change it in one place.

# file server

Node.js as a File Server

The Node.js file system module allows you to work with the file system on your computer.

To include the File System module, use the require() method:

The fs.readFile() method is used to read files on your computer.

var http = require('http');
var fs = require('fs');
http.createServer(function (req, res) {
  fs.readFile('demofile1.html', function(err, data) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write(data);
    return res.end();
  });
}).listen(8080);
<html>
<body>
<h1>My Header</h1>
<p>My paragraph.</p>
</body>
</html>

Create a file in the same folder

demofile1.html

var url = require('url');
var adr = 'http://localhost:8080/default.htm?year=2022&month=may';
var q = url.parse(adr, true);

console.log(q.host); //returns 'localhost:8080'
console.log(q.pathname); //returns '/default.htm'
console.log(q.search); //returns '?year=2022&month=may'

var qdata = q.query; //returns an object: { year: 2022, month: 'may' }
console.log(qdata.month); //returns 'may'
# url module

Node.js URL Module

The URL module splits up a web address into readable parts.

# file server code

Now we know how to parse the query string, and we learned how to make Node.js behave as a file server.
Lets combine the two, and serve the file requested by the client.

Create two html files and save them in the same folder as your node.js files.

Node.js File Server

<!DOCTYPE html>
<html>
<body>
<h1>Winter</h1>
<p>I love the snow!</p>
</body>
</html>
<!DOCTYPE html>
<html>
<body>
<h1>Summer</h1>
<p>I love the sun!</p>
</body>
</html>

summer.html

winter.html

http://localhost:8080/summer.html

http://localhost:8080/winter.html

# solution

Solution

Node.js File Server

var http = require('http');
var url = require('url');
var fs = require('fs');

http.createServer(function (req, res) {
  var q = url.parse(req.url, true);
  var filename = "." + q.pathname;
  fs.readFile(filename, function(err, data) {
    if (err) {
      res.writeHead(404, {'Content-Type': 'text/html'});
      return res.end("404 Not Found");
    } 
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write(data);
    return res.end();
  });
}).listen(8080);

{npm}

the package manager used by Node.js applications - you can find a ton of modules here, so you don’t have to reinvent the wheel

The website https://npmjs.com 

// package.json
{
 "name": "@me/test-app",
 "version": "1.0.0",
 "description": "",
 "main": "index.js",
 "scripts": {
   "test": "echo \"Error: no test specified\" && exit 1",
   "start": "node index.js",
   "sayHi": "echo 'Hello!'"
 },
 "author": "",
 "license": "ISC"
}
# npm init && package.json

NPM init

npm init
// package.json
{
 "name": "@me/test-app",
 "version": "1.0.0",
 "description": "",
 "main": "index.js",
 "scripts": {
   "test": "echo \"Error: no test specified\" && exit 1",
   "start": "node index.js",
   "sayHi": "echo 'Hello!'"
 },
 "author": "",
 "license": "ISC"
}
# npm init && package.json

CMD line

npm run test
// package.json
{
 "name": "@me/test-app",
 "version": "1.0.0",
 "description": "",
 "main": "index.js",
 "scripts": {
   "test": "echo \"Error: no test specified\" && exit 1",
   "start": "node index.js",
   "sayHi": "echo 'Hello!'"
 },
 "author": "",
 "license": "ISC"
}
# npm init && package.json

CMD line

npm install
// package.json
{
 "name": "@me/test-app",
 "version": "1.0.0",
 "description": "",
 "main": "index.js",
 "scripts": {
   "test": "echo \"Error: no test specified\" && exit 1",
   "start": "node index.js",
   "sayHi": "echo 'Hello!'"
 },
 "license": "ISC",
  "dependencies": {
    "<module>": "^5.29.2",
  },
 "author": ""
}
# npm init && package.json

CMD line

npm install <module> --save 
# Where <module> is the name of the module you want to install
// package.json
{
 "name": "@me/test-app",
 "version": "1.0.0",
 "description": "",
 "main": "index.js",
 "scripts": {
   "test": "echo \"Error: no test specified\" && exit 1",
   "start": "node index.js",
   "sayHi": "echo 'Hello!'"
 },
 "license": "ISC",
  "devDependencies": {
    "<module>": "^5.29.2",
  },
 "author": ""
}
# npm init && package.json

CMD line

npm install <module> --save-dev
# Where <module> is the name of the module you want to install

a collection of the dependencies that are used in development of your application - the modules that you use to build it, but don't need to use when it's running. This could include things like testing tools, a local server to speed up your development, and more.

# npm init && package.json

CMD line

npm install <module> --global 
npm install <module> -g        #short-hand
# Where <module> is the name of the module you want to install globally

One caveat with global modules is that, by default, npm will install them to a system directory, not a local one. With this as the default, you'll need to authenticate as a privileged user on your system to install global modules.

Environment Variables

# npm init && package.json

NPX

npm install -g npx
npx <module> # replace <module> with the package 
# you want to run from package.json
npx cowsay aMaZiNg #running an uninstalled package using npx
npx https://gist.github.com/nTrajkovik/60db0ca94e318ceb68bfff29f4b14d8c

{node.js}

global variables && more modules

VS

Read-Eval-Print-Loop (REPL) 

# nodeJs
node
global
process
console
Ctrl + C // two times to exit
global == window
dev console
npm install -g nodemon 
nodemon server.js
npx nodemon server.js

nodemon

Events & callbacks

# nodeJs
const { EventEmitter } = require('events');
// EventEmitter is a class
const eventEmitter = new EventEmitter();
// we instantiate classes

// register an event
eventEmitter.on('eat', () => {
  console.log('🥩 nom-nom');
});

// raise an event
eventEmitter.emit('eat');
eventEmitter.emit('eat');
   window.addEventListener()

Events & callbacks

# nodeJs
const { EventEmitter } = require('events');
// EventEmitter is a class
const eventEmitter = new EventEmitter();
// we instantiate classes

// register an event
eventEmitter.on('eat', (food) => {
  console.log(`${food} nom-nom`);
});

// raise an event
eventEmitter.emit('eat', ' 🥩 ');
eventEmitter.emit('eat', ' 🍕 ');
   window.addEventListener()

Blocking & non-blocking

# nodeJs
const fs = require('fs');

const txt = fs.readFileSync('./hello.txt', 'utf-8');

console.log(txt);

console.log('Emergency thing to print!');
const fs = require('fs');

fs.readFile('./hello.txt', 'utf-8', (err, txt) => {
	console.log(txt);
});

console.log('Emergency thing to print!');

Blocking & non-blocking

# nodeJs
const fs = require('fs').promises;

async function printFile() {
    const txt = await fs.readFile('./index.html', 'utf-8');
    console.log(txt);
}
printFile();
console.log('Emergency thing to print!');
const fs = require('fs').promises;
// top level await available from Node v14.3
const txt = await fs.readFile('./index.html', 'utf-8');
console.log(txt);
console.log('Emergency thing to print!');

os module

# nodeJs
const os = require('os');

var totalMemory = os.totalmem();
var freeMemory = os.freemem();

console.log('Total Memory: ' + totalMemory);
console.log(`Free Memory: ${freeMemory}`);
// Template string
// ES6 / ES2015 : ECMAScript 6

nodemailer - we can send emails
reset password, welcome to the platform etc. all are sent using some sort of mailer

# nodeJs
var nodemailer = require('nodemailer');

var transporter = nodemailer.createTransport({
  service: 'gmail',
  auth: {
    user: 'youremail@gmail.com',
    pass: 'yourpassword'
  }
});

var mailOptions = {
  from: 'youremail@gmail.com',
  to: 'myfriend@yahoo.com',
  subject: 'Sending Email using Node.js',
  text: 'That was easy!'
};

transporter.sendMail(mailOptions, function(error, info){
  if (error) {
    console.log(error);
  } else {
    console.log('Email sent: ' + info.response);
  }
});

upload files - formidable module

# nodeJs
npm install formidable

Demo time

Create upload form

# nodeJs
var http = require('http');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
  res.write('<input type="file" name="filetoupload"><br>');
  res.write('<input type="submit">');
  res.write('</form>');
  return res.end();
}).listen(8080);

Parse uploaded file

# nodeJs
var http = require('http');
var formidable = require('formidable');

http.createServer(function (req, res) {
  if (req.url == '/fileupload') {
    var form = new formidable.IncomingForm();
    form.parse(req, function (err, fields, files) {
      res.write('File uploaded');
      res.end();
    });
  } else {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
    res.write('<input type="file" name="filetoupload"><br>');
    res.write('<input type="submit">');
    res.write('</form>');
    return res.end();
  }
}).listen(8080);

Save file

# nodeJs
var http = require('http');
var formidable = require('formidable');
var fs = require('fs');

http.createServer(function (req, res) {
  if (req.url == '/fileupload') {
    var form = new formidable.IncomingForm();
    form.parse(req, function (err, fields, files) {
      var oldpath = files.filetoupload.filepath;
      var newpath = './' + files.filetoupload.originalFilename;
      fs.rename(oldpath, newpath, function (err) {
        if (err) throw err;
        res.write('File uploaded and moved!');
        res.end();
      });
 });
  } else {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
    res.write('<input type="file" name="filetoupload"><br>');
    res.write('<input type="submit">');
    res.write('</form>');
    return res.end();
  }
}).listen(8080);

Let's code

# nodeJs
/*
 * Write a server which has the following routes:
 * localhost:8080/get-image -> returns the uploaded image 
 * 		or error message if no image uploaded
 * localhost:8080/ -> returns upload file form
 * localhost:8080/upload-image -> accepts a file via forms 
 * 		and saves it - if image exists, remove it
*/

{mongodb}

a source-available cross-platform document-oriented database program. Classified as a NoSQL database program, MongoDB uses JSON-like documents with optional schemas. 

# storing variable

Storing data in a global variable

Serving static pages for users - as you have learned - can be suitable for landing pages, or for personal blogs. However, if you want to deliver personalized content you have to store the data somewhere.

const users = [];

http.createServer(function (req, res) {
  
  if (req.url == "/users" && req.method == 'post') {
    const user = req.body;
    users.push({
      name: user.name,
      age: user.age,
    });
  }
  res.write(`Successfully registered`);
  res.end();
}).listen(8080);

# storing variable

Storing in variable

Let’s take a simple example: user signup. You can serve customized
content for individual users or make it available for them after
identification only.
If a user wants to sign up for your application, you might want to
create a route handler to make it possible:

# storing var

This way you can store the users in a global variable, which will reside
in memory for the lifetime of your application.

Using this method might be problematic for several reasons:
• RAM is expensive,
• memory resets each time you restart your application,
• if you don’t clean up, sometimes you’ll end up with stack overflow.

# storing file

Storing data in a file

The next thing that might come up in your mind is to store the data in files. If we store our user data permanently on the file system, we can avoid the previously listed problems.

const fs = require('fs');

http.createServer(function (req, res) {
  
  if (req.url == "/users" && req.method == 'post') {
    const user = req.body;
    fs.appendToFile(
		'./users.txt', 
        JSON.stringify({ name: user.name, age: user.age }),
		(err) => {
   			res.send('successfully registered');
   		}
	);
  }
  res.write(`Successfully registered`);
  res.end();
}).listen(8080);

# storing file

Storing in file

This way we won’t lose user data, not even after a server reset. This solution is also cost efficient, since buying storage is cheaper than buying RAM.

# storing file

Unfortunately storing user data this way still has a couple of flaws:
 

• Appending is okay, but think about updating or deleting.

• If we’re working with files, there is no easy way to access them in parallel (system-wide locks will prevent you from writing, like editing files while vscode is open).

• When we try to scale our application up, we cannot split files (you can, but it is way beyond the level of this tutorial) in between servers

This is where real databases come into play.

You might have already heard that there are two main kinds of
databases: NoSQL and SQL.

NoSQL

SQL

npm install mongodb
npm list mongodb

To use MongoDB we need to install a MongoDB driver

Atlas - fully managed DaaS (Database as a Service)

Clusters - a set of nodes where copies of the database are stored

Demo time

const { MongoClient } = require('mongodb')

const uri = 'mongodb+srv://sourcemx:sourcemx@cluster0.4om6h.mongodb.net/?retryWrites=true&w=majority';

async function main() {
  const client = new MongoClient(uri);
  
  try {
    await client.connect();
    console.log('Connection success!');
  } catch (e) {
    console.error(e);
  } finally {
    await client.close()
  }
}

main().catch(console.error);
# mongodb
const { MongoClient } = require('mongodb')

const uri = 'mongodb+srv://sourcemx:sourcemx@cluster0.4om6h.mongodb.net/?retryWrites=true&w=majority';

async function main() {
  const client = new MongoClient(uri);
  
  try {
    await client.connect();
    console.log('Connection success!');
    await listDatabases(client);
  } catch (e) {
    console.error(e);
  } finally {
    await client.close()
  }
}

main().catch(console.error);

async function listDatabases(client) {
  const databasesList = await client.db().admin().listDatabases();
  console.log(databasesList);
}
# mongodb
const { MongoClient } = require('mongodb')

const uri = 'mongodb+srv://sourcemx:sourcemx@cluster0.4om6h.mongodb.net/?retryWrites=true&w=majority';

async function main() {
  const client = new MongoClient(uri);
  
  try {
    await client.connect();
    console.log('Connection success!');
    await addTodoNote(client, {title: 'Shopping list', description: 'Steak, Pizza, Fries'});
  } catch (e) {
    console.error(e);
  } finally {
    await client.close()
  }
}

main().catch(console.error);

async function addTodoNote(client, todoNote) {
  const result = await client.db('notes').collection('todos').insertOne(todoNote);
  console.log(`New note created with id ${result.insertedId}`);
}
# mongodb

  await client.db('notes').collection('todos').insertOne(todoNote);
  await client.db('notes').collection('todos').find().toArray();
  await client.db('notes').collection('todos')
			.deleteOne(
    { _id: ObjectId("563237a41a4d68582c2509da") },
  );
  await client.db('notes').collection('todos')
    		.updateOne(
    { _id: ObjectId("563237a41a4d68582c2509da") },
    newNoteObject
  );

# mongodb

Let's code

{HTTP request methods}

GET    POST    PUT    DELETE

  • GET

The GET method requests a representation of the specified resource. Requests using GET should only retrieve data.

  • POST

The POST method submits an entity to the specified resource, often causing a change in state or side effects on the server.

  • DELETE

The DELETE method deletes the specified resource.

  • PUT

The PUT method replaces all current representations of the target resource with the request payload.

PATCH, CONNECT, OPTIONS, HEAD, TRACE...

window.fetch('http://localhost:8080/note', {
    method: 'POST', 
    body: JSON.stringify(
      { title: 'dog says', description: 'woof woof'}
    ),
})
# PRESENTING CODE

POST

Postman is an API platform for building and using APIs. Postman simplifies each step of the API lifecycle and streamlines collaboration so you can create better APIs - faster.

https://www.postman.com/downloads/

{nodejs + mongodb}

Request body data and updating

Let's code now!

{REST-API}

Representational State Transfer
REST determines how the API looks like.
It is a set of rules that developers follow when they create their API.

  • One of these rules states that you should be able to get a piece of data (called a resource) when you link to a specific URL.

Rules

  • Use nouns instead of verbs in endpoint paths

Rules

  • Accept and respond with JSON

Rules

  • Allow filtering, sorting, and pagination

Rules

{express}

fast, unopinionated, minimalist web framework for Node.js. It simplifies the server creation process that is already available in Node. 

npm install express --save
# express

Adding Express to your project is only an NPM install away:

 const express = require('express');
 const app = express();
 const port = 3000;
 app.get('/', (request, response) => {
 	response.send('Hello from Express!');
 });
 app.listen(port, (err) => {
   if (err) {
   	return console.log('something bad happened', err);
   }
   console.log(`server is listening on ${port}`);
 });
npm init // in a new folder 
# express
 const express = require('express');
 const app = express();
 const port = 3000;
 app.get('/', (request, response) => {
 	response.send('Hello from Express!');
 });
 app.listen(port, (err) => {
   if (err) {
   	return console.log('something bad happened', err);
   }
   console.log(`server is listening on ${port}`);
 });

The biggest difference what you have to notice here is that Express
by default gives you a router. You don’t have to check manually for
the URL to decide what to do, but instead, you define the application’s routing with app.get, app.post, app.put, etc. They are translated to the corresponding HTTP verbs.

{FE + BE + DB}

Have FE + BE in same folder

# Code Structure

Have FE + BE in same folder

                        - separate repos

# Code Structure

Let's put them together!

Start both projects

# Code Structure
npm run dev
npm run start

FE

BE

package.json
package.json
const CartProvider = ({ children }) => {
  const [pizzaProducts, setPizzaProducts] = useState([]);
  useEffect(function(){
      axios.get('http://localhost:8080/pizzas').then(response => {
      setPizzaProducts(response.data);
      })
  },[])
# calling our BE

Replace fake data with real data

  • Cross Origin Requests are requests from one origin to another origin.
    By default browsers block cross origin requests as a security feature.

CORS

Whitelisting

# ADMIN PANEL

Base64

Way of encoding binary data to a string. We can then decode it (or let the browser decode it by using the img tag)

{project structuring}
& other important stuff

most Node.js frameworks don’t come with a fixed directory structure and it might be challenging to get it right from the beginning.

Fundamental rules

Organize your Files Around Features, Not Roles​

1.

2.

Minimize Logic in index.js (server.js) Files

3.

Variable & Function naming conventions

# unwritten rules

Fundamental rules

Organize your Files Around Features, Not Roles​

1.

# unwritten rules

Fundamental rules

Minimize Logic in index.js Files (server.js)

2.

# unwritten rules

Fundamental rules

Variable & Function naming conventions

3.

# unwritten rules

Good read: Source

Fundamental Rules

  • Add Clear and Concise Comments to Your Code

4.

5.

Portability

6.

Reusability and Scalability

# more rules

7.

 

Don’t use synchronous functions

Fundamental Rules

  • Add Clear and Concise Comments to Your Code

4.

# more rules
  • working in a team
  • forgetting own code
  • adding todos in comments
  • too much === bad
  • clear and concise
  • don't explain the code, explain the why

sometimes good code does not need comments

Fundamental Rules

5.

Portability

# more rules
  • use variables and don't write hard-coded configurations (no localhost inside the code) use process.env.HOST_NAME

Fundamental Rules

6.

Reusability and Scalability

# more rules
  • essential design goal
  • if a module/service/component works, we can use it again and not code it from scratch every time
  • cut down on development cost and resources
  • scalability means a user can demand a change, new features, improvements. Ability to easily incorporate updates is essential in software

Fundamental Rules

# more rules

7.

 

Don’t use synchronous functions

  • synchronous functions tie up executing processes untill they finish
  • in high-traffic even a microsecond counts
  • on initial setup it's okay to have synchronous
  • if given choice sync vs async - always go async

Fundamental Rules

  • Use try-catch

8.

9.

Use promises

10.

Handle exceptions properly

# more rules

11.

use .ENV

{important concepts}

some important practical concepts

we love acronyms

KISS

Keep It Simple Stupid
other variants:
Keep it short and simple
Keep it simple and straightforward
Occam’s Razor - The simplest solution is most likely the correct solution
Albert Einstein’s – “Make everything as simple as possible but not simpler”
Leonardo Da Vinci’s – “Simplicity is the ultimate sophistication”
Ludwig Mies Van Der Rohe’s – “Less is more”

DRY

Donot Repeat Yourself

When the DRY principle is applied successfully, a modification of any single element of a system does not require a change in other logically unrelated elements.

WET

Write Everything Twice

When we abstract too much when a requirement comes in we tend to use the same abstraction rather than code it in another (better) way.

SoC

Separation of Concerns
A program that embodies SoC well is called a modular program

e.g.
HTML, CSS, JavaScript
e.g.
pizzas.service.js, orders.service.js, tags.service.js

YAGNI

You ain’t gonna need it

 

"Always implement things when you actually need them, never when you just foresee that you need them."

DTSTTCPW
"do the simplest thing that could possibly work"

NodeJs - SMX Academy - 2022

By jeger12345

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NodeJs - SMX Academy - 2022

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