How to add delay after promise.all in for loop

user_2455259 0
Viewed 41

I have eg: 20 (can be dynamic) promises which makes API call. I am dividing into batches of 10. like [[p1,... p10], [p11,... p20] ...]

I am having for loop on it and executing p1 to p10 promises using promise.all like that then p11 to p20 etc..

 let res: any = [];
 batch.forEach(item => {
     Promise.all(item).then(values => {
        res = [...res, ...values];
     });
 })

Now Here I want to add delay between p1..p10 to p11..p20. What is the way for this in Javascript ?

promise node.js asynchronous javascript
3 Answers
async function timeOut(delay) {
 return new Promise(resolve => setTimeout(() => resolve(true), delay))
}

async function wrapper() {
  let res: any = [];
  for(let item of batch) {
    const values = await Promise.all(item)
    res.push(...values);
    await timeOut(2000)
  }
}

wrapper()
user_150846450

Inside a Array.forEach method you can't await promises so the best approach is to use a common for...of loop.

Here i declared a sleep function to implement the delay and then i just wrote your logic but using a normal loop

const sleep = async sec => new Promise((resolve, _reject) => setTimeout(resolve, sec * 1000))

;(async () => {
    let res: any = [];
    for(const item of batch) {
        const values = await Promise.all(item);
        res.push(...values)
        await sleep(2) // n of seconds you want
    }
})()
user_172645700

If you want a serial execution with wait, you can follow below using reduce with serial promise chaining.

const wait = (timer) => new Promise((resolve) => setTimeout(resolve, timer * 1000));

let res: any = [];
batch.reduce((acc, item) => {
  // chain last item promise in loop
  return acc.then(() => 
    Promise.all(item).then(values => {
      res = [...res, ...values];
    })
    // one items promise resolved wait 10sec
    .then(() => wait(10))
  );
}, Promise.resolve());
user_24354730
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