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#ege-academy-nodejs @rbung @yagong
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#ege-academy-nodejs @rbung @yagong
How to write your own module
module.exports = function() { // export a default function
// lib logic
}
module.exports = { // export several functions
foo: function() {},
bar: function() {},
}#ege-academy-nodejs @rbung @yagong
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#ege-academy-nodejs @rbung @yagong
stream
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What is it for ?
🚀 Handle large amounts data in a very efficient way 😎
Â
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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);
});#ege-academy-nodejs @rbung @yagong
https://github.com/rbung/ExerciceTransactionAnalyser
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Node.js academy - Core concepts
By yagong
