Using promise function inside Javascript Array map

Having an array of objects [obj1, obj2]

I want to use Map function to make a DB query (that uses promises) about all of them and attach the results of the query to each object.

[obj1, obj2].map(function(obj){
  db.query('obj1.id').then(function(results){
     obj1.rows = results
     return obj1
  })
})

Of course this doesn't work and the output array is [undefined, undefined]

What's the best way of solving a problem like this? I don't mind using other libraries like async

Map your array to promises and then you can use Promise.all() function:

var promises = [obj1, obj2].map(function(obj){
  return db.query('obj1.id').then(function(results){
     obj1.rows = results
     return obj1
  })
})
Promise.all(promises).then(function(results) {
    console.log(results)
})

You are not returning your Promises inside the map function.

[obj1, obj2].map(function(obj){
  return db.query('obj1.id').then(function(results){
     obj1.rows = results
     return obj1
  })
})

Example using async/await:

const mappedArray = await Promise.all(
  array.map(p => {
    return getPromise(p).then(i => i.Item);
  })
);

You can also do for await instead of map, and resolve your promises inside of it as well.

You can also use p-map library to handle promises in map function.

> Useful when you need to run promise-returning & async functions multiple times with different inputs concurrently.

> This is different from Promise.all() in that you can control the concurrency and also decide whether or not to stop iterating when there's an error.