promise.js

// create
// starts as pending
const arrived = true;
const ride = new Promise((resolve, reject) => {
  // executor (callback function)
  if (arrived) {
    resolve('arrived');
  } else {
    reject('failed');
  }
});

// consume
ride
  .then(value => {
    console.log(value);
  })
  .catch(error => {
    console.log(error);
  })
  .finally(() => {
    console.log('always runs');
  })

const codeBlocker = () => {
  // ! blocking
  // let i = 0
  // while (i < 1000000000) { i++; }

  // ! async blocking
  // return new Promise((resolve, reject) => {
  //   let i = 0;
  //   while (i < 1000000000) { i++; }
  //   resolve('loops done');
  // })

  // non-blocking - must be inside resolve.then callback
  return Promise.resolve().then(v => {
    let i = 0;
    while (i < 1000000000) { i++; }
    return 'loops done';
  })
}
codeBlocker().then(console.log);

// promise.all
const promise1 = Promise.resolve('Hello world');
const promise2 = 10;
const promise3 = new Promise((resolve, reject) =>
  setTimeout(resolve, 2000, 'Goodbye')
);
const promise4 = fetch('https://jsonplaceholder.typicode.com/users').then(res => res.json());
Promise.all([promise1, promise2, promise3, promise4]).then(console.log);