javascript - promise 延迟实现

Question

我尝试通过这种方式实现 Promise 的延迟:

function postAndSetContentfulId (client, code) {
  return delay().then(_ => {
    return postToContentful(client, code).then(setCode)
  })
}

function delay () {
  let multipler = Math.floor((count++) / 100) + 1
  let milliseconds = multipler * 2000
  return new Promise(resolve => setTimeout(() => resolve(), milliseconds))
}

我需要延迟第三方 API 调用以避免速率限制问题。这似乎并没有真正起作用，因为我全部都被一堆执行了。

Answer 1

我有一个几年前编写的简单的速率有限的 promise 队列，它对我很有用

const rateLimited = perSecond => {
    const milliSeconds = Math.floor(1000 / perSecond);
    let promise = Promise.resolve(Date.now());
    return fn => promise.then(lastRun => {
        const wait = Math.max(0, milliSeconds + lastRun - Date.now());
        promise = promise.then(() => new Promise(resolve => setTimeout(resolve, wait))).then(() => Date.now());
        return promise.then(() => fn());
    });
};

const example = rateLimited(2); // 2 per second for the example
let allPromises = Array.from({length:10}, (_, i) => i)
    .map(v => example(() => Promise.resolve(v)));
console.time('Elapsed');
console.log('Started - should take 5 seconds');
Promise.all(allPromises).then(results => {
    console.log(results);
    console.timeEnd('Elapsed');
});

对于您的代码，您可以使用 rateLimited ，例如

const q = rateLimited(20); // 20 per second limit for example
function postAndSetContentfulId(client, code) {
    return q(() => postToContentful(client, code).then(setCode));
}