Calculating sum of multiple async callbacks

Question

I am still learning Javascript properly and read a few threads on here about asynchronity (1 2). Unfortunately, I have still trouble to find a solution to my problem. I am calling an API in async fashion and would like to create a sum out of the response that I am receiving of multiple async calls.

Let's say I want my code to perform an action if my "sum" has a value of 40. Async call "A" returns 6, async call "B" returns 8, and so on until we finally reach the value of 40. How can I create such a sum, as my calls are all async? Would it require to write each async result to a database and pull the value up in the next async call? Is there a better solution for this?

Thank you for your help.

EDIT: To make things easier to understand I will add some source code:

Webhook.js

router.post('/', (req, res, next) => {
  if (middleware.active)
    middleware.handle(req.body) // <--- this gives me one result
  res.sendStatus(200)
});

Basically, I will receive multiple webhook calls. "middleware.handle" will send an API call to third party application. I want to take the result from that API call and add it to the result of another API call from another webhook request.

As you can see, I don't know when my webhook will be triggered, neither how many times it will be triggered before reaching my desired total of 40.

You would have to use async wait and promise state "fulfilled". However, please add your code here to give correct suggestions — rootkonda, Feb 24 '20 at 10:13
Database, or some other form of persistence in between posts is what's needed here. — danh, Mar 03 '20 at 04:40
Any advice what would be the best solution? I am not storing much data. Just some simple sums. — paaax, Mar 03 '20 at 05:51

score 0 · Answer 1 · answered Feb 24 '20 at 10:13

0

You can use Promise.all([apiCallOne, apiCallTwo]).then(values => sum(values)) sum being a function that sums an array of numbers

answered Feb 24 '20 at 10:13

Jacob

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5
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score 0 · Answer 2 · answered Feb 24 '20 at 10:23

You can await for both in a do/while loop then do the rest of the logic

async function myFunc() {
   let valA = 0;
   let valB = 0;
   do {
      valA += await fetch('https://api.url.com/a');
      valB += await fetch('https://api.url.com/b');
   } while((valA + valB) < 40 );

You can also do each one in its do/while loop if you want to request value from one only at a time then check condition.

Calculating sum of multiple async callbacks

2 Answers2