How to make for loop wait for certain period for every interval till array is completed

Question

I am building a small prototype like feeds. I have an array of many items. For each item in an array, I need to make an API call and load results.

It's a performance issue if I have too many records and too many APi calls to make.

I am trying to stop my loop for every 2-3 API calls for 100ms and then resume execution till array is completed.

I made a POC but it doesn't work well. Can you help me with whats wrong in below code

// work in progress

var arr = ["val1", "val2", "val3", "val4", "val5", "val6"];

let breakCounter;
async function seriesAPI(arr) {
  breakCounter = 2;
  for (let i = 0; i <= arr.length; i++) {
    if (breakCounter - arr.indexOf(arr[i]) === 0) {
      await interval(arr[i]);

      breakCounter = breakCounter + 2;
    } else {
      makeAPI(arr[i])
      //console.log(arr[i]);
    }
  }
}

function makeAPI(val) {
  console.log(val);
  // fetch(url, {method: 'POST', body: JSON.stringify(arr[i])}).then(res => console.log(res));
}

function interval(arrval) {
  console.log("Buffer time");
  setTimeout(() => {
    makeAPI(arrval)
  }, 1000);
}

seriesAPI(arr);

Do you want to restrict doing all "many" parallel API calls to doing just 2-3 at a time? I'd suggest you to consider [throttling](https://stackoverflow.com/questions/20253425/throttle-and-queue-up-api-requests-due-to-per-second-cap) — Parzh from Ukraine, Dec 02 '21 at 13:44

score 1 · Answer 1 · answered Dec 02 '21 at 13:57

I suggest you to wrap your interval method as Promise and call it on loop iteration when it's needed before request fetching.

var arr = ["val1", "val2", "val3", "val4", "val5", "val6"];

async function seriesAPI(arr) {
  for (let i = 0; i <= arr.length; i++) {
    if (!(i % 3)) { // on each 3rd iteration
      await interval(100); // make 100ms delay
    }
    makeAPI(arr[i])
    // console.log(arr[i]);
  }
}

function makeAPI(val) {
  console.log(val);
  // fetch(url, {method: 'POST', body: JSON.stringify(arr[i])}).then(res => console.log(res));
}

function interval(ms) {
  return new Promise(r => setTimeout(r, ms)); 
  // auto-resolve after [ms] milliseconds  
}

seriesAPI(arr);

What's with the undefined? – mplungjan Dec 02 '21 at 14:13 — mplungjan, Dec 02 '21 at 14:13

score 0 · Accepted Answer · answered Dec 02 '21 at 13:45

No need for async

var arr = ["val1", "val2", "val3", "val4", "val5", "val6"];
let cnt = 0;

function makeAPI() {
  if (cnt >= arr.length) return 
  console.log(arr[cnt]);
  // fetch(url, {method: 'POST', body: JSON.stringify(arr[cnt])})
  //  .then(res => setTimeout(makeAPI,cnt%3 === 0 ? 3000: 100));
  cnt++;
  setTimeout(makeAPI,cnt%3 === 0 ? 3000: 100);
}

makeAPI()

How to make for loop wait for certain period for every interval till array is completed

2 Answers2