en.javascript.info/8-async/05-promise-api/article.md

Promise API

There are helpful static methods in the Promise class. There are only 4 of them, so we'll quickly cover them here.

Promise.all

The method to run many promises in parallel and wait till all of them are ready.

The syntax is:

let promise = Promise.all(iterable);

It takes an iterable object with promises, for instance an array and returns a new promise that resolves with the array of their results when all of them are settled, or rejects with the first encountered error if any.

For instance:

// loads 3 scripts in parallel and returns an array of them
Promise.all([
  loadScript('/article/promise-api/one.js'),
  loadScript('/article/promise-api/two.js'),
  loadScript('/article/promise-api/three.js')
]).then(scripts => {
  alert(`scripts loaded: ${scripts}`);
});

• the returned promise awaits for al

In the previous chapter we saw how to run things sequentially. Promises also

• Promise.all
• Promise.race
• Promise.reject
• Promise.resolve

Let's meet more functions and methods for promises.

Keywords async and await provide a more elegant way to write the code using promises.

Async functions

The async function is like a regular one, but it wraps a returned value in a Promise.

Nowadays, promises are de-facto standard for asynchronous actions, when we need to