How to use it with promise string label in javascript

I am trying to use a promise as below.

let promiseArray: [string, Promise<unknown>][] = [];
for(const a of array)
{
   const promise = new Promise(() => {this.repository.getRepository<a.entity>.find()});
   promiseArray.push([a.entityName, promise]);
}

And the result of the code above is:

result : [
    ['EntityName', [{},{},{}]],
    ['EntityName2', [{},{},{}]],
     ....
]

But I don't know how can I apply promiseArray to promise.all.

await Promise.all(promiseArray)
          .then((res) => {
            console.log(res);
          })
          .catch((e) => console.error(e));

I tried the above, but it didn't work, and I tried promiseArray.map((pm)=>pm[1]), but I couldn't map the value of pm[0].

It looks like you're populating your array wrong. From your code, it looks like you're using TypeORM, and that .find() is async (returns a promise). So, you don't need to wrap it in another promise. Try filling the array like this:

let promiseArray: [string, Promise<unknown>][] = [];
for(const a of array)
{
   const promise = this.repository.getRepository<a.entity>.find();
   promiseArray.push([a.entityName, promise]);
}

Then, all you need to do is a .map() to get the second value in the array, which is the promise returned by .find():

await Promise.all(promiseArray.map(el => el[1]));

If you need to pass the .entityName along with the promise's result, then map each element to its .find() promise, then add the entity name to the result in a .then(). This creates a single promise per element in array and can be simply passed to Promise.all():

const promiseArray: [Promise<[string, unknown]>][] = array.map(el => this.repository.getRepository<a.entity>.find().then(res => [el.entityName, res]));
const results = await Promise.all(promiseArray);

Promise.all accepts an array of promises, but you have an array of -

Array<[String, Promise]>

You will need to construct the array of promises differently -

const promiseArray: Promise<Array<[string, unknown]>> = []

for (const a of array) {
   const promise = new Promise((resolve, reject) => {
     // ...
   })
   .then(result => [a.entityName, result]) // ✅ 
   promiseArray.push(promise)
}

Now you can use Promise.all -

Promise.all(promisesArray).then(...)

Results in -

[
  ['EntityName', <promise result>],
  ['EntityName2', <promise result>],
  ...
]

Here's a functioning example -

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const randPromise = () =>
  new Promise(r =>
    setTimeout(r, 1000, Math.random() * 100 | 0)
  )
  
const labels = ["a", "b", "c", "d"]
  
const promises = []

for (const label of labels)
  promises.push(randPromise().then(value =>
    [label, value]
  ))
  
Promise.all(promises)
.then(JSON.stringify)
.then(console.log)
.catch(console.error)
// [["a",53],["b",25],["c",22],["d",53]]

<!-- end snippet -->

Instead of using the for..of loop, many find it easier to use an array's map function -

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const randPromise = () =>
  new Promise(r =>
    setTimeout(r, 1000, Math.random() * 100 | 0)
  )
  
const labels = ["a", "b", "c", "d"]
  
Promise.all(labels.map(label =>
  randPromise().then(value => [label, value])
))
.then(JSON.stringify)
.then(console.log)
.catch(console.error)
// [["a",90],["b",20],["c",76],["d",60]]

<!-- end snippet -->

Every then expression has an equivalent async..await representation. This approach uses fewer nested lambdas and therefore a bit easier to digest -

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const randPromise = () =>
  new Promise(r =>
    setTimeout(r, 1000, Math.random() * 100 | 0)
  )
  
const labels = ["a", "b", "c", "d"]
  
Promise.all(labels.map(async label =>
  [label, await randPromise()]
))
.then(JSON.stringify)
.then(console.log)
.catch(console.error)
// [["a",90],["b",20],["c",76],["d",60]]

<!-- end snippet -->