异步 function + await + setTimeout 的组合

Question

I am trying to use the new async features and I hope solving my problem will help others in the future. This is my code which is working:

  async function asyncGenerator() {
    // other code
    while (goOn) {
      // other code
      var fileList = await listFiles(nextPageToken);
      var parents = await requestParents(fileList);
      // other code
    }
    // other code
  }

  function listFiles(token) {
    return gapi.client.drive.files.list({
      'maxResults': sizeResults,
      'pageToken': token,
      'q': query
    });
  }

The problem is, that my while loop runs too fast and the script sends too many requests per second to the google API. Therefore I would like to build a sleep function which delays the request. Thus I could also use this function to delay other requests. If there is another way to delay the request, please let me know.

Anyway, this is my new code which does not work. The response of the request is returned to the anonymous async function within the setTimeout, but I just do not know how I can return the response to the sleep function resp. to the initial asyncGenerator function.

  async function asyncGenerator() {
    // other code
    while (goOn) {
      // other code
      var fileList = await sleep(listFiles, nextPageToken);
      var parents = await requestParents(fileList);
      // other code
    }
    // other code
  }

  function listFiles(token) {
    return gapi.client.drive.files.list({
      'maxResults': sizeResults,
      'pageToken': token,
      'q': query
    });
  }

  async function sleep(fn, par) {
    return await setTimeout(async function() {
      await fn(par);
    }, 3000, fn, par);
  }

I have already tried some options: storing the response in a global variable and return it from the sleep function, callback within the anonymous function, etc.

Answer 1

Your sleep function does not work because setTimeout does not (yet?) return a promise that could be await ed. You will need to promisify it manually:

function timeout(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}
async function sleep(fn, ...args) {
    await timeout(3000);
    return fn(...args);
}

Btw, to slow down your loop you probably don't want to use a sleep function that takes a callback and defers it like this. I recommend:

while (goOn) {
  // other code
  var [parents] = await Promise.all([
      listFiles(nextPageToken).then(requestParents),
      timeout(5000)
  ]);
  // other code
}

which lets the computation of parents take at least 5 seconds.

Answer 2

快速单行、内联方式

 await new Promise(resolve => setTimeout(resolve, 1000));

Answer 3

Since Node 7.6 , you can combine the functions promisify function from the utils module with setTimeout() .

Node.js

const sleep = require('util').promisify(setTimeout)

Javascript

const sleep = m => new Promise(r => setTimeout(r, m))

Usage

(async () => {
    console.time("Slept for")
    await sleep(3000)
    console.timeEnd("Slept for")
})()

Answer 4

setTimeout is not an async function, so you can't use it with ES7 async-await. But you could implement your sleep function using ES6 Promise :

function sleep (fn, par) {
  return new Promise((resolve) => {
    // wait 3s before calling fn(par)
    setTimeout(() => resolve(fn(par)), 3000)
  })
}

Then you'll be able to use this new sleep function with ES7 async-await:

var fileList = await sleep(listFiles, nextPageToken)

Please, note that I'm only answering your question about combining ES7 async/await with setTimeout , though it may not help solve your problem with sending too many requests per second.

---

Update: Modern node.js versions has a buid-in async timeout implementation, accessible via util.promisify helper:

const {promisify} = require('util');
const setTimeoutAsync = promisify(setTimeout);

Answer 5

Update 2021

await setTimeout finally arrived with Node.js 16, removing the need to use util.promisify() :

import { setTimeout } from 'timers/promises';

(async () => {
  const result = await setTimeout(2000, 'resolved')
  // Executed after 2 seconds
  console.log(result); // "resolved"
})()

Official Node.js docs: Timers Promises API (library already built in Node)

Answer 6

If you would like to use the same kind of syntax as setTimeout you can write a helper function like this:

const setAsyncTimeout = (cb, timeout = 0) => new Promise(resolve => {
    setTimeout(() => {
        cb();
        resolve();
    }, timeout);
});

You can then call it like so:

const doStuffAsync = async () => {
    await setAsyncTimeout(() => {
        // Do stuff
    }, 1000);

    await setAsyncTimeout(() => {
        // Do more stuff
    }, 500);

    await setAsyncTimeout(() => {
        // Do even more stuff
    }, 2000);
};

doStuffAsync();

I made a gist: https://gist.github.com/DaveBitter/f44889a2a52ad16b6a5129c39444bb57

Answer 7

var testAwait = function () {
    var promise = new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Inside test await');
        }, 1000);
    });
    return promise;
}

var asyncFunction = async function() {
    await testAwait().then((data) => {
        console.log(data);
    })
    return 'hello asyncFunction';
}

asyncFunction().then((data) => {
    console.log(data);
});

//Inside test await
//hello asyncFunction

Answer 8

This is my version with nodejs now in 2020 in AWS labdas

const sleep = require('util').promisify(setTimeout)

async function f1 (some){
...
}

async function f2 (thing){
...
}

module.exports.someFunction = async event => {
    ...
    await f1(some)
    await sleep(5000)
    await f2(thing)
    ...
}

Answer 9

await new Promise(resolve => setTimeout(() => { resolve({ data: 'your return data'}) }, 1000))

Answer 10

await setTimeout(()=>{}, 200);

如果您的 Node 版本是 15 及更高版本，则可以使用。

Answer 11

The following code works in Chrome and Firefox and maybe other browsers.

function timeout(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}
async function sleep(fn, ...args) {
    await timeout(3000);
    return fn(...args);
}

But in Internet Explorer I get a Syntax Error for the "(resolve **=>** setTimeout..."

Answer 12

Made a util inspired from Dave 's answer

Basically passed in a done callback to call when the operation is finished.

// Function to timeout if a request is taking too long
const setAsyncTimeout = (cb, timeout = 0) => new Promise((resolve, reject) => {
  cb(resolve);
  setTimeout(() => reject('Request is taking too long to response'), timeout);
});

This is how I use it:

try {
  await setAsyncTimeout(async done => {
    const requestOne = await someService.post(configs);
    const requestTwo = await someService.get(configs);
    const requestThree = await someService.post(configs);
    done();
  }, 5000); // 5 seconds max for this set of operations
}
catch (err) {
  console.error('[Timeout] Unable to complete the operation.', err);
}

Answer 13

How to Log all the responses at once?

async function sayHello(name) {
  let greet = `Hey! ${name} very nice to meet you bud.`;
  setTimeout(() => {
    return {
      greet,
      createdAt: new Date(),
    };
  }, 1000);
}

const response1 = async () => await sayHello("sounish");
const response2 = async () => await sayHello("alex");
const response3 = async () => await sayHello("bill");

async function getData() {
  const data1 = await sayHello("sounish");
  const data2 = await sayHello("alex");
  const data3 = await sayHello("bill");
  return { data1, data2, data3 };
}

Promise.all([sayHello("sounish"), sayHello("alex"), sayHello("bill")]).then(
  (allResponses) => {
    console.log({ allResponses });
  }
);

getData().then((allData) => {
  console.log({ allData });
});

Answer 14

I leave this code snippet here for someone who wants fetch API call (eg get clients) with setTimeout :

const { data } = await new Promise(resolve => setTimeout(resolve, 250)).then(() => getClientsService())
setName(data.name || '')
setEmail(data.email || '')

Answer 15

I would like to point out a robust extension to Promise.all . A rather elegant solution that works with one promise to be time-limited only is to race the promise with a timeout (such as new Promise((resolve) => setTimeout(resolve, timeout)) ).

await new Promise.race([myPromise, timeoutPromise])

will continue as soon as one of the promises finished. myPromise then can internally await a different timeout, or simply make use of Promise.all

const timeout = ms => new Promise((resolve) => setTimeout(resolve, ms));
await Promise.race([
    Promise.all([myPromise, timeout(500)]),
    timeout(5000)
]);

The result is an asynchronous call that does not run more often than twice a second, with a timeout of 5 seconds in case of some (network/server?) error.

Moreover, you can make this very versatile and customizable function as such:

function callWithTimeout(promise, msTimeout=5000, throws=false) {
    const timeout = ms => new Promise((resolve, reject) =>
        setTimeout(throws ? reject : resolve, ms));
    await Promise.race([
        //depends whether you want to wait there or just pass the promise itself
        Promise.all([promise, timeout(500)]), 
        timeout(msTimeout)
    ]);
}
    

Which ultimately lets you customize the timeout time and the whether the promise should succeed or throw on timeout. Having such robust general implementation can save you a lot of pain in the future. You can also set a string instead of boolean as throws and bind this variable to the reject for custom error message: reject.bind(undefined, throws)

Note that you should not pass your promise with await:

const myPromise = async x => x;
//will never time out and not because myPromise will finish immediatelly
callWithTimeout(await myPromise(), 200, true); 
//will possibly timeout after 200 ms with an exception 
callWithTimeout(myPromise(), 200, true); 

Answer 16

With the marked answer I had a lint error [no-promise-executor-return] so I found here the corrected version, using curly brackets in order to make explicit the intention of not returning anything:

const timeout = (ms) =>
  new Promise(resolve => {
    setTimeout(resolve, ms)
  })

Answer 17

This is a quicker fix in one-liner.

Hope this will help.

// WAIT FOR 200 MILISECONDS TO GET DATA //
await setTimeout(()=>{}, 200);