mostaza-corso-async

mostaza-corso-async.md

Async/Await, Promises, callbacks

Event driven architecture, event loop

Callback

• Come funzionano (esempio)

const fs = require('fs');

const data = fs.readFileSync('test.txt');
console.log(data);

const fs = require('fs');

try {
  const data = fs.readFileSync('test.txt');
  console.log(data);
} catch (err) {
  console.error(err);
}

const fs = require('fs');

const data = fs.readFile('test.txt', function (err, data) {
  if (err) {
     return console.error(err);
  }
  console.log(data);
});

const fs = require('fs');

const copyFile = function(source, destination, next) {
  fs.readFile(source, function(err, data) {
    if (err) {
       return throw err;
    }
    fs.writeFile (savPath, data, function(err) {
       if (err) {
          throw err;
       }
       console.log('Bella! Ho copiato il file!');
    });
  });
};

• Blocking/non blocking (synchronous and single thread)
• Dove si usano: I/O in node, altro

Promises

• Come funzionano (esempio)

const { promisify } = require('util');
const fs = require('fs');

// Definisco fs.readFile come promise
const readFileAsync = promisify(fs.readFile);

readFileAsync('test.txt')
  .then(function (data) {
    console.log('Ho questo bellissimo testo il testo:', data);
  })
  .catch(function (err) {
    console.log('Error:', err);
  });

• Cenni XMLHttpRequest/AJAX e Fetch

fetch('https://api.github.com/users/mmazzarolo/repos?sort=updated')
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.log('Error:', err))

• Librerie: Bluebird, Q, Promise polyfills

Async/Await

• Come funzionano (esempio)

const res = await fetch('https://api.github.com/users/mmazzarolo/repos?sort=updated')
const jsonRes = await res.json();
console.log(jsonRes)

const callApi = async (url) => {
  try {
    const res = await fetch(url)
    const jsonRes = await res.json();
    console.log(jsonRes)
  } catch (err) {
    console.log('Error:', err)
  }
}

• Generators
• Limiti

Functional Programming

• Functions are first class citizens
• Functions declaration and invocation examples
• Pure Functions
  • No side-effects
  • Predictable output
  • Avoid mutations
• Immutability (Object.assign, Object.freeze, deep immutability, const vs let)
• Map, filter, reduce
• Lodash/Ramda