Promise.race和Promise.any使用示例详解

Promise.race(iterable)

const promise1 = new Promise((resolve, reject) => {
    setTimeout(resolve, 500, 'promise 1 resolved');
});
const promise2 = new Promise((resolve, reject) => {
    setTimeout(reject, 100, 'promise 2 rejected');
});
const promise3 = new Promise((resolve, reject) => {
    setTimeout(resolve, 200, 'promise 3 resolved')
});
(async () => {
    try {
        let result = await Promise.race([promise1, promise2, promise3]);
        console.log(result);
    } catch (err) {
        console.error(err);
    }
})();
  // 输出- "promise 2 rejected"
  // 尽管promise1和promise3可以解决，但promise2拒绝的速度比它们快。
  // 因此Promise.race方法将以promise2拒绝

function getUserInfo(user) {
  return new Promise((resolve, reject) => {
    // had it at 1500 to be more true-to-life, but 900 is better for testing
    setTimeout(() => resolve("user data!"), Math.floor(900*Math.random()));
  });
}
function showUserInfo(user) {
  return getUserInfo().then(info => {
    console.log("user info:", info);
    return true;
  });
}
function showSpinner() {
  console.log("please wait...")
}
function timeout(delay, result) {
  return new Promise(resolve => {
    setTimeout(() => resolve(result), delay);
  });
}
Promise.race([showUserInfo(), timeout(300)]).then(displayed => {
  if (!displayed) showSpinner();
});

function timeout(delay) {
  let cancel;
  const wait = new Promise(resolve => {
    const timer = setTimeout(() => resolve(false), delay);
    cancel = () => {
      clearTimeout(timer);
      resolve(true);
    };
  });
  wait.cancel = cancel;
  return wait;
}
function doWork() {
  const workFactor = Math.floor(600*Math.random());
  const work = timeout(workFactor);
  const result = work.then(canceled => {
    if (canceled)
      console.log('Work canceled');
    else
      console.log('Work done in', workFactor, 'ms');
    return !canceled;
  });
  result.cancel = work.cancel;
  return result;
}
function attemptWork() {
  const work = doWork();
  return Promise.race([work, timeout(300)])
    .then(done => {
      if (!done)
        work.cancel();
      return (done ? 'Work complete!' : 'I gave up');
  });
}
attemptWork().then(console.log);

const _ = require('lodash')
async function batchRequests(options) {
    let query = { offset: 0, limit: options.limit };
    do {
        batch = await model.findAll(query);
        query.offset += options.limit;
        if (batch.length) {
            const promise = doLongRequestForBatch(batch).then(() => {
                // Once complete, pop this promise from our array
                // so that we know we can add another batch in its place
                _.remove(promises, p => p === promise);
            });
            promises.push(promise);
            // Once we hit our concurrency limit, wait for at least one promise to
            // resolve before continuing to batch off requests
            if (promises.length >= options.concurrentBatches) {
                await Promise.race(promises);
            }
        }
    } while (batch.length);
    // Wait for remaining batches to finish
    return Promise.all(promises);
}
batchRequests({ limit: 100, concurrentBatches: 5 });

Promise.any(iterable);

const promise1 = new Promise((resolve, reject) => {
  setTimeout(reject, 100, 'promise 1 rejected');
});
const promise2 = new Promise((resolve, reject) => {
  setTimeout(resolve, 400, 'promise 2 resolved at 400 ms');
});
const promise3 = new Promise((resolve, reject) => {
  setTimeout(resolve, 700, 'promise 3 resolved at 800 ms');
});
(async () => {
  try {
    let value = await Promise.any([promise1, promise2, promise3]);
    console.log(value);
  } catch (error) {
    console.log(error);
  }
})();
//Output - "promise 2 resolved at 400 ms"