NodeJs, Promises not waiting

Question

I have this function that should make 300 requests for a web page (for benchmarking), however the Promise.all is not waiting for those requests to finish before outputting an empty array, any ideas?

function requestLoop(){

  var resultSet= [];

  // options.requests = 300
  // options.url = http://localhost/

  for(var c=1;c<=options.requests; c++){

    http.get(options.url, function(res){

    //  resultSet.push( { request: c, statusCode: res.statusCode});

      resultSet.push(new Promise(function(res){ return { request: c, statusCode: res.statusCode}; }));

    });

  }

  Promise.all(resultSet).then(function(){
    console.log(resultSet);
  });

  return;

}

Promise is bluebird and http is the normal http package

Possible duplicate of [How do I return the response from an asynchronous call?](http://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — Yury Tarabanko, Apr 21 '17 at 10:46
You are creating promises in callback.When `Promise.all(resultSet)` is executed non of promises was created. — Yury Tarabanko, Apr 21 '17 at 10:48
I would disagree, I am not using AJAX and that question only refers to a single request, I am attempting to make multiple and bring the results together. — B1scuit, Apr 21 '17 at 10:48
`http.get` returns promise too.. You should be pushing that in array! — Rayon, Apr 21 '17 at 10:48
It doesn't matter what is the source of async in your code: ajax or http.get or whatever. The reason is the same. — Yury Tarabanko, Apr 21 '17 at 10:49
@YuryTarabanko — I do not think OP is returning the response.. He is using Promise but implementation is wrong.... — Rayon, Apr 21 '17 at 11:03
@Rayon No difference between returning or pushing to external array. — Yury Tarabanko, Apr 21 '17 at 11:11
And BTW no difference if you are returning a Promise from callback or anything else. This is still returning from asynchronous call. :) — Yury Tarabanko, Apr 21 '17 at 11:15

score 4 · Accepted Answer · edited Apr 21 '17 at 15:17

Promise is being pushed in array in callback. Hence By the time Promise.all invokes, array is empty([])

Push new Promise in array within loop itself, not in callback

function requestLoop() {
  var resultSet = [];
  for (var c = 1; c <= options.requests; c++) {
    (function(c) {
      resultSet.push(new Promise(function(resolve) {
        http.get(options.url, function(res) {
          resolve({
            request: c,
            statusCode: res.statusCode
          });
        });
      }));
    })(c);
  }
  Promise.all(resultSet).then(function() {
    console.log(resultSet);
  });
}

NodeJs, Promises not waiting

1 Answers1