How can I fetch an array of URLs without Promise.all?

Question

This question is the same as How can I fetch an array of URLs with Promise.all? except that I want an answer that does not use Promise.all. ¹

The array of URLs:

urls = ['https://jsonplaceholder.typicode.com/todos/2',
        'https://jsonplaceholder.typicode.com/todos/3']

The JSONs of the URLs:

{"userId":1,"id":2,"title":"quis ut nam facilis et officia qui",
 "completed":false}
{"userId":1,"id":3,"title":"fugiat veniam minus","completed":false}

The goal is to get an array of objects, where each object contains the title value from the corresponding URL.

To make it a little more interesting, I will assume that there is already an array of names that I want the array of titles to be merged with:

namesonly = ['two', 'three']

The desired output is an array of objects:

[{"name":"two","loremipsum":"quis ut nam facilis et officia qui"},
{"name":"three","loremipsum":"fugiat veniam minus"}]

where I have changed the attribute name title to loremipsum.

¹ The specific reason I want a solution not using Promise.all is that I want JavaScript code that works in Postman scripts. The latter don't (yet) support promises natively, at the time of writing.

The reason is in the footnote. Still, the question itself has nothing to do with Postman. — Henke, Jun 01 '21 at 16:27
Ah, I missed the footnote. So, What does postman actually do when fetching, in that case? — VLAZ, Jun 01 '21 at 16:29
This risks getting off-topic but ..., Postman uses something called _pm objects_ instead of promises, unfortunately. — Henke, Jun 01 '21 at 16:30
I think it's relevant because maybe there is an alternative solution. However, I need to know how exactly it handles async in order to figure out if there is one and if so, what is it. — VLAZ, Jun 01 '21 at 16:32
Is [this](https://learning.postman.com/docs/writing-scripts/script-references/postman-sandbox-api-reference/#sending-requests-from-scripts) how one should make requests with Postman? — VLAZ, Jun 01 '21 at 16:34
Here is a [link saying pm.sendRequest returns a _pm object_ instead of a promise](https://github.com/postmanlabs/postman-app-support/issues/3927). I _can_ use promises in Postman scripts (since it is just JavaScript), but certain native functions can not be called from within the "callback" of a Promise, most notably `pm.visualizer.set()`. — Henke, Jun 01 '21 at 16:38

Henke · Accepted Answer · 2021-06-02T10:54:27.810

The following solution relies on the second Stack Snippet of this helpful answer. ¹

const namesonly = ['two', 'three'];
const urls = ['https://jsonplaceholder.typicode.com/todos/2',
  'https://jsonplaceholder.typicode.com/todos/3'];

const titles = [];
let countDown = urls.length;
urls.forEach((url, index) => {
  asynchronousCall(url, title => {
    titles[index] = title;
    if (--countDown === 0) { // Callback for ALL starts on next line.
      const names = namesonly.map(value => ({ name: value }));
      const fakeLatins = titles.map(value => ({ loremipsum: value }));
      const result =
        names.map((item, i) => Object.assign({}, item, fakeLatins[i]));
      console.log('result:\n' + JSON.stringify(result));
    }
  });
});
function asynchronousCall (url, callback) {
  console.log('Starting fetch for "' + url + '".');
  fetch(url).then(response => response.json()).then(responseBody => {
    console.log(url.slice(-1) + ': ' + responseBody.title + ' ...');
    console.log('... fetch for ' + url + ' completed!');
    callback(responseBody.title); // Individual callback.
  });
}

.as-console-wrapper { max-height: 100% !important; top: 0; }

References

¹ I have deliberately left a lot of printouts in the code. The purpose is to make it easier to see what is happening and in what order. Anyone considering to use the code should of course remove some or all of the printouts.

How can I fetch an array of URLs without Promise.all?

1 Answers1

References

Linked