Unable to Resolve Promise in forEach

Question

This is the code where I'm calling a function

masterCredsResponse.data.forEach((masterCred) => {
  // Check Login status
  masterCredsArray.push({
    master: masterCred.parent,
    loginCheck: Promise.resolve(getSessionID()())
  })
})

Here I get

loginCheck: Promise { <pending> }

I'm seeing a lot of questions on this topic but unable to understand how to get it done. When I don't use loop but call it separately then it works like

let loginCheckReponse =  await getSessionID()()

But i use this method in a loop that doesn't work

loginCheck: await getSessionID()() // Doesn't work

if `getSessionID()()` results in a Promise, then `Promise.resolve(getSessionID()())` doesn't do anything useful (like wait for it to settle) — Jaromanda X, Nov 25 '22 at 06:48
You misunderstand what `Promise.resolve` does. It wraps an already found value inside of a new `Promise` that immediately `resolve`s, meaning the data is able to be accessed. It doesn't mean that it doesn't make it a `Promise` anymore. You still need to either `await` or `.then` the `Promise` — Samathingamajig, Nov 25 '22 at 06:48
And then moves to next iteration without returning actual response from getSessionID func — Iqra Moazzama, Nov 25 '22 at 06:49
the clue is where you say `then it works like` ... that's what you need to do in a `for` loop, not in a `forEach` callback — Jaromanda X, Nov 25 '22 at 06:49
There is some good information about this here: https://stackoverflow.com/questions/40328932/javascript-es6-promise-for-loop — Boguz, Nov 25 '22 at 07:04

Jake Fried · Answer 1 · 2022-11-25T07:06:34.413

@Samathingamajig is right about Promise.resolve. Also, you can't run await inside of the forEach without making the callback async.

The most basic fix would be adding an async to the callback and an await to the promise. But you then wouldn't be able to ergonomically wait for the array to finish processing.

masterCredsResponse.data.forEach(async (masterCred) => {
  masterCredsArray.push({
    master: masterCred.parent,
    loginCheck: Promise.resolve(getSessionID())
  })
})

You can use map and Promise.all to make sure you block execution properly. Note that they will all occur in parallel:

const masterCredPromises = masterCredsResponse.data.map(
  async (masterCred) => ({
    master: masterCred.parent, 
    loginCheck: await getSessionId()
  })
);
const masterCredsArray = await Promise.all(masterCredPromises);

Hope that helps!

So you mean the solution will Promise.all() will work faster then others ? due to parallel in nature — Iqra Moazzama, Nov 25 '22 at 07:12

score 1 · Answer 2 · answered Nov 25 '22 at 07:07

1

masterCredsResponse.data.forEach( async (masterCred) => {
  let loginCheckReponse =  await getSessionID()()
  // Check Login status
  masterCredsArray.push({
    master: masterCred.parent,
    loginCheck: loginCheckReponse
  })
})

answered Nov 25 '22 at 07:07

Rajan Karmaker

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Unable to Resolve Promise in forEach

2 Answers2