Question

154

How to use `Array#map` within `Promise.all` in JavaScript

rated 0 times [ 157] [ 3] / answers: 1 / hits: 24337 / 7 Years ago, sun, april 16, 2017, 12:00:00

I am trying to create a Promise.all with an array of items. So if I create it like this it works fine

Promise.all([

  Query.getStuff(items[0]),

  Query.getStuff(items[1])

]).then(result => console.log(result))

If I try to create the Promise.all like this, it doesn't work

Promise.all([

    items.map(item => Query.getStuff(item))

]).then(result => console.log(result))

The then block is run before the Query.getStuff(item). What am I missing?

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shannon

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2 Years ago

answered 7 Years ago blaisep · Accepted Answer

You should be writing

Promise.all(items.map(...))

instead of

Promise.all([ items.map(...) ])

Array#map returns an array, which means that the way you wrote your code originally, you were actually passing a multidimensional array to Promise.all — as in [ [promise1, promise2, ...] ] — instead of the expected one-dimensional version [promise1, promise2, ...].

Revised Code:

Promise.all(

    items.map(item => Query.getStuff(item))

).then(result => console.log(result))