How to add delay in nodejs - node.js

Question

i am calling a 3rd party API in a loop in my nodejs application. Basically I have a list, am iterating through the list and calling the 3rd party API.
The 3rd party API is very slow and cannot handle more than 3 requests. I have been advised to add some delay.
Please can someone advise how to add delay in this scenario.
var promises = [];
promises = rids.map((rid,j) => {
// 3rd party API
// getServiceDetailsApi is wrapper around 3rd party API
return getServiceDetailsApi(rid)
});
// console.log(promises);
Promise.all(promises)
.then(res => {
// console.log('promise complete..' + res.length)
var responses = [];
res.map((response,i) => {
var serviceAttributesDetail = {};
// console.log(response);
serviceAttributesDetails = response.data.serviceAttributesDetails;
serviceAttributesDetail.rid = serviceAttributesDetails.rid;
responses = responses.concat(serviceAttributesDetail);
})
// Add more logic above
return Promise.all(responses);
})

Answer 1

If one request at a time is enough, you can try this way:
'use strict';
(async function main() {
try {
const responses = [];
for (const rid of rids) {
const response = await getServiceDetailsApi(rid);
responses.push({ rid: response.data.serviceAttributesDetails.rid });
}
console.log(responses);
} catch (err) {
console.error(err);
}
})();

Answer 2

If your restriction is about having a maximum of 3 concurrent requests to that API, here is a possibility (untested though, there might be typos, and I didn't think the rejection handling):
const cfgMaxApiCalls = 3;
...
function getServiceDetailsApi() {...}
...
const rids = ...
...
const promisedResponses = new Promise((generalResolve) => {
let currentCalls = 0; // to know how many calls in progress
const responses = []; // the output of the general promise
// this chains promises, ensuring we do an API call only when another one finished
const consumer = (response) => {
responses.push(response); // first remember the data
// stop condition: nothing more to process, and all current calls have resolved
if (!rids.length && !currentCalls--) {
return generalResolve(responses);
}
// otherwise make a new call since this one's done
return getServiceDetailsApi(rids.shift()).then(consumer);
};
// start the process for maximum `cfgMaxApiCalls` concurrent calls
for (; currentCalls < cfgMaxApiCalls && rids.length; currentCalls++) {
getServiceDetailsApi(rids.shift()).then(consumer);
}
});
promisedResponses.then((res) => {
// here `res` === your code's `res`
// and by the way, Array.prototype.concat is not asynchronous,
// so no need to Promise.all(responses) at the end ;)
});