javascript - How to flatten a promise.all response - Stack Overflow

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I have a list of products and for each product im making an api call to get the products subscription.

   const subscriptions = await Promise.all(products.flatMap((p: any) => {
        const { username, password } = p.credentials;
        return GetSubscription(username, password);
    }));
    console.log(subscriptions);

Actual:

[ [ {}, {}, {}, ] ]

now you can see i have a double nested array here and i don't need the outer array, how can i flatten this array, i assumed using flatMap here might help me but it did not.

Expected:

[ {}, {}, {}, ]

Ofcourse i could simply do subscriptions[0] but im trying to avoid that if possible.

I have a list of products and for each product im making an api call to get the products subscription.

   const subscriptions = await Promise.all(products.flatMap((p: any) => {
        const { username, password } = p.credentials;
        return GetSubscription(username, password);
    }));
    console.log(subscriptions);

Actual:

[ [ {}, {}, {}, ] ]

now you can see i have a double nested array here and i don't need the outer array, how can i flatten this array, i assumed using flatMap here might help me but it did not.

Expected:

[ {}, {}, {}, ]

Ofcourse i could simply do subscriptions[0] but im trying to avoid that if possible.

• javascript
• node.js
• typescript

Share Improve this question Follow asked Jan 27, 2020 at 10:36 KayKay 19.7k7272 gold badges184184 silver badges301301 bronze badges 2

• 3 Array.prototype.flat() - developer.mozilla/en-US/docs/Web/JavaScript/Reference/… – Bloatlord Commented Jan 27, 2020 at 10:38
• ah the simple .flat does not make my api call GetSubscription so it did not work – Kay Commented Jan 27, 2020 at 10:55

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 8

Use the spread operator

async function func() {
  return 'A';
}

(async() => {
  const [...ret] = await Promise.all([
    func(),
    func(),
    func(),
  ]);

  console.log(ret);
})();

Or

async function func() {
  return 'A';
}

(async() => {
  const ret = await Promise.all([
    func(),
    func(),
    func(),
  ]);

  console.log(ret.reduce((tmp, x) => [...tmp, x], []));
})();

---

As you said in your ment, specifying ES2019 in your tsconfig, you can use Array.flat :

async function func() {
  return 'A';
}

(async() => {
  const ret = await Promise.all([
    func(),
    func(),
    func(),
  ]);

  console.log(ret.flat());
})();

This should help you.

const input = [[{}, {}, {}], [{"hi": "bye"}]];


console.log(input.flat());

Array.flatMap() is the same as Array.map().flat(). So await Promise.all(Array.map().flat()) will be applied to the result of flat. When the map callback is asynchronous you need to resolve the result of map before calling flat. In that case you would need to use (await Promise.all(Array.map())).flat().

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