Node.js Academy

Core concepts 😎

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REQUIRE AND MODULE

CODE EXAMPLE

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package resolution

require('./bar') // this will load file ./bar.js

require('bar')
// this is looking module in node_modules
// first ./node_modules/bar
// then ../node_modules/bar
// then ../../node_modules/bar
// until /node_modules/bar

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How JS handles concurrency

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Stack and frame

  • Each function call creates a frame
  • A stack is a set of frames

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EVENTLOOP JS

simple version

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CODE EXAMPLE

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EVENTLOOP NODE

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Best practices under eventloop model

  • keep each stack execution rapid: no blocking synchronous function call
  • keep each stack small: use as async function when possible

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Asynchronous in NodeJS

Callback, Promess, Async/Await

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Code example

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NodeJS Module

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What is a module in NodeJS?

  • Consider modules to be the same as JavaScript libraries
  • A set of functions you want to include in your application
  • Each file .js is a module

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How to use a Module

const http = require('http') // buildin module
const lib = require('./lib') // local module
const toto = require('./toto.json') // json file

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How to write your own module

module.exports = function() { // export a default function
  // lib logic
}

module.exports = { // export several functions
  foo: function() {},
  bar: function() {},
}

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Some core modules

fs, cpu, stream

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File system: FS

const fs = require('fs')
const readFile = require('util').promisify(fs.readFile)

readFile(`${__dirname}/module-usage/toto.json`, 'utf-8')
  .then(data => console.log(data))
  .catch(err => console.error(err))

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system stats: CPU

npx vtop

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stream

Official documentation

Node.js Streams: Everything you need to know

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What is it for ?

🚀 Handle large amounts data in a very efficient way 😎

 

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4 types of Stream

  • Readable
  • Writable
  • Duplex
  • Transform

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Some examples

// Read a big file and write the content into the http response

const fs = require('fs');
const server = require('http').createServer();

server.on('request', (req, res) => {
  const src = fs.createReadStream('./big.file');
  src.pipe(res);
});

server.listen(8000);


// Compress a big file

const gzip = require('zlib').createGzip();
const fs = require('fs');

const inp = fs.createReadStream('The.Matrix.1080p.mkv');
const out = fs.createWriteStream('The.Matrix.1080p.mkv.gz');

inp.pipe(gzip).pipe(out);

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Pipe operator

Event emitters

readableSrc
  .pipe(transformStream1)
  .pipe(transformStream2)
  .pipe(finalWrtitableDest)
readable.on('data', (chunk) => {
  writable.write(chunk);
});

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https://github.com/rbung/ExerciceTransactionAnalyser

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Node.js academy - Core concepts

By Rodolphe BUNG

Source: yagong

Node.js academy - Core concepts

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