Node / JS

Class.js

// from: https://medium.com/backticks-tildes/understanding-method-chaining-in-javascript-647a9004bd4f

class Arithmetic {
  constructor() {
    this.value = 0;
  }
  sum(...args) {
    this.value = args.reduce((sum, current) => sum + current, 0);
    return this;
  }
  add(value) {
    this.value = this.value + value;
    return this;
  }
  subtract(value) {
    this.value = this.value - value;
    return this;
  }
  average(...args) {
    this.value = args.length
      ? (this.sum(...args).value) / args.length
      : undefined;
    return this;
  }
}

a = new Arithmetic()
a.sum(1, 3, 6)   // => { value: 10 } 
  .subtract(3)   // => { value: 7 }
  .add(4)        // => { value: 11 }
  .value         // => 11 

// Console Output
// 11

Promise Chain.js

// from: https://stackoverflow.com/questions/49033694/how-to-use-then-in-node-js
// video: https://www.youtube.com/watch?v=_JOP8rcDjJE
// video pt-BR: https://www.youtube.com/watch?v=7Bs4-rqbCQc

function one(){
  return new Promise(resolve => {
    setTimeout(() => {
      resolve('one');
     }, 1000);
  });
}

function two(){
  return new Promise(resolve => {
    setTimeout(() => {
      resolve('two');
     }, 1000);
  });
}

function three(){
  return new Promise((resolve, reject) => {
    setTimeout(() => {
			resolve('three');
      // reject(new Error('three'));
     }, 1000);
  });
}

one()
  .then((msg) => {
    console.log('first msg:', msg);
    return two();
  })
  .then((msg) => {
    console.log('second msg:', msg);
    return three();
  })
  .then((msg) => {
    console.log('third msg:', msg);
  })
  .catch((error) => {
    console.error('Something bad happened:', error.toString());
  });

// OR

async function run() {
  await one();
  await two();
  three();
}
run();

Promise For.js

// from: https://lavrton.com/javascript-loops-how-to-handle-async-await-6252dd3c795/
function delay() {
  return new Promise(resolve => setTimeout(resolve, 300));
}

async function delayedLog(item) {
  // notice that we can await a function
  // that returns a promise
  await delay();
  console.log(item);
}
async function processArray(array) {
  for (const item of array) {
    await delayedLog(item);
  }
  console.log('Done!');
}

processArray([1, 2, 3]);

uuid.js

	const UUID = Math.random().toString(36).slice(-8);

Good Video about Promises: https://www.youtube.com/watch?v=52JDIMoTTzI