How to make it so that I can execute say 10 promises at a time in javascript to prevent rate limits on api calls?

Question

I have 1000 records that need to hit an API endpoint that is rate limited. I want to make it so that there is only 5 calls on the URL at any given time so that I am not making 1

Answer 1

Use waterfall pattern without a library and use a race condition to resolve on each iteration with reduce. And you can limit the number of calls by specifying the length of the array in Array.from.

var promise = Array.from({ length: 5 }).reduce(function (acc) {
  return acc.then(function (res) {
    return run().then(function (result) {
      res.push(result);
      return res;
    });
  });
}, Promise.resolve([]));


var guid = 0;
function run() {
  guid++;
  var id = guid;
  return new Promise(resolve => {
    // resolve in a random amount of time
    setTimeout(function () {
      console.log(id);
      resolve(id);
    }, (Math.random() * 1.5 | 0) * 1000);
  });
}