How to make subsequent http requests asynchronously inside a while loop without using promises and async/await?

Question

I have a service that is written in Node and sends the request to get a list of teams for a specific city to another API service.

Request params:

• city
• page
• per_page

Response body:

• page
• per_page
• more
• teams

per_page by default is set to 1000 but the number of teams is much greater than 1000 and some teams are not returned in the response. I need all the teams though. For some reasons I am not going to specify here, I do not want to change per_page param, but what I want to do is to send the first request and check if more in the response body is true (meaning there are more teams), I extract teams from the response body and add it to the final result, increase page param and send the request with params:

{
  "page": "2",
  "city": "chicago",
  "per_page": 1000, 
 }

I keep doing that until more header is false.

The service is written in Node and I use the request package for sending HTTP requests. Initially, I wanted to use while loop:

function teamsInCity(city, page, result, callback) {
 let more = true;

  while(more) {
  // send the request
  // extract teams into the result array
  // check if there is more
  // send another request
  // keep sending requests and appending teams until more is false
  } 
  // return the final result with all the teams
}

But that didn't work because while loop sends the request and keeps executing the next line of code without waiting for the response. So I solved it with recursion and it works. But I need it to be tail call optimized and I am not sure but I think Node doesn't support that but I might be wrong.

Is there a way to send requests inside of while loop without using async/await and promises?

Below is my working function with recursion:

function teamsInCity(city, page, result, callback) {
  request.get({
    url: 'my_service' + '/teams',
    qs: { 'city' : city, 'page': page, 'per_page': 1000 },
    json: true
  }, function(err, response, body) {
    if (err) { return callback(err); }

    result = result.concat(body.teams);

    if (body.more) {
      page++;
      return teamsInCity(city, page, result, callback);
    }
    return callback(null, result);
  });
}

And here is the route that calls teamsInCity()

router.get('/:city', function(req, res) {
  var data = {teams: []};
  myService.teamsInCity(req.params.city, 1, [], function(err, teams) {
    if (err) {
      logger.error('Error while retrieving teams in ' + req.params.city);
    }
    data.teams = _.sortBy(teams, 'name');
    res.send(data);
  });
});

Thank you!

Answer 1

You could use the async library, and the whilst function. I don't think this will make your Stack Overflow ;-)

For example:

const async = require("async");

function teamsInCity(city, callback) {
    let result = [];
    let page = 0;
    let more = true;
    async.whilst(
        () => more,
        (callback2) => {
            request.get({
                url: 'my_service' + '/teams',
                qs: { 'city' : city, 'page': page++, 'per_page': 1000 },
                json: true
            }, (err, response, body) => {
                if (err) { 
                    callback2(err); 
                    console.error(`teamsInCity: Error occurred: ${err.message}`);
                } else {
                    console.log(`teamsInCity: Page#: ${page}, Team count: ${body.teams.length}, More pages: ${body.more}`);
                    more = body.more;
                    result = result.concat(body.teams);
                    callback2(null, result);
                }
            })
        },
        (err, result) => {
            if (err) console.error("Final callback error: ", err.message);
            if (!err) console.log("Final callback result: ", result);
            callback(err, result);
        }
    );
}