Promise API

let promise = Promise.all(iterable);

Promise.all([
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 3000)), // 1
  new Promise((resolve, reject) => setTimeout(() => resolve(2), 2000)), // 2
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 1000))  // 3
]).then(alert); // 1,2,3 promise が準備できた時: 各 promise は配列の中身に寄与します

let urls = [
  'https://api.github.com/users/iliakan',
  'https://api.github.com/users/remy',
  'https://api.github.com/users/jeresig'
];

// 各 url を promise の fetch(github url) へマップする
let requests = urls.map(url => fetch(url));

// Promise.all はすべてのジョブが解決されるまで待ちます
Promise.all(requests)
  .then(responses => responses.forEach(
    response => alert(`${response.url}: ${response.status}`)
  ));

let names = ['iliakan', 'remy', 'jeresig'];

let requests = names.map(name => fetch(`https://api.github.com/users/${name}`));

Promise.all(requests)
  .then(responses => {
    // すべてのレスポンスが用意できたら HTTP ステータスコードが見られます
    for(let response of responses) {
      alert(`${response.url}: ${response.status}`); // 各 url で 200 が表示されます
    }

    return responses;
  })
  // それぞれの中身を読むために、レスポンスの配列を response.json() の配列にマッピングします
  .then(responses => Promise.all(responses.map(r => r.json())))
  // すべての JSON応答が解析され、"user" はそれらの配列です。
  .then(users => users.forEach(user => alert(user.name)));

Promise.all([
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 1000)),
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Whoops!")), 2000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 3000))
]).catch(alert); // Error: Whoops!

Promise.all([
  fetch('/template.html'),
  fetch('/style.css'),
  fetch('/data.json')
]).then(render); // render メソッドはすべての fetch の結果が必要

let urls = [
  'https://api.github.com/users/iliakan',
  'https://api.github.com/users/remy',
  'https://no-such-url'
];

Promise.allSettled(urls.map(url => fetch(url)))
  .then(results => { // (*)
    results.forEach((result, num) => {
      if (result.status == "fulfilled") {
        alert(`${urls[num]}: ${result.value.status}`);
      }
      if (result.status == "rejected") {
        alert(`${urls[num]}: ${result.reason}`);
      }
    });
  });

[
  {status: 'fulfilled', value: ...レスポンス...},
  {status: 'fulfilled', value: ...レスポンス...},
  {status: 'rejected', reason: ...エラーオブジェクト...}
]

if (!Promise.allSettled) {
  const rejectHandler = reason => ({ status: 'rejected', reason });

  const resolveHandler = value => ({ status: 'fulfilled', value });

  Promise.allSettled = function (promises) {
    const convertedPromises = promises.map(p => Promise.resolve(p).then(resolveHandler, rejectHandler));
    return Promise.all(convertedPromises);
  };
}

let promise = Promise.race(iterable);

Promise.race([
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 1000)),
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Whoops!")), 2000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 3000))
]).then(alert); // 1

let promise = Promise.any(iterable);

Promise.any([
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Whoops!")), 1000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 2000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 3000))
]).then(alert); // 1

Promise.any([
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Ouch!")), 1000)),
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Error!")), 2000))
]).catch(error => {
  console.log(error.constructor.name); // AggregateError
  console.log(error.errors[0]); // Error: Ouch!
  console.log(error.errors[1]); // Error: Error!
});

let promise = new Promise(resolve => resolve(value));

let cache = new Map();

function loadCached(url) {
  if (cache.has(url)) {
    return Promise.resolve(cache.get(url)); // (*)
  }

  return fetch(url)
    .then(response => response.text())
    .then(text => {
      cache.set(url,text);
      return text;
    });
}

let promise = new Promise((resolve, reject) => reject(error));