Map async functions over an array

Question

I am trying to map an async function over an array, I hope to achieve such effect:

const result = orgs.map(org => 
  f(org)
    .then(res => return res))
// now result should be an array of res
console.log(result)

This would not work, so I tried another way:

const result = []
orgs.map(org => 
  f(org)
    .then(res => result.push(res)))
// now result should be an array of res
console.log(result)

Still, this won't work.

But I can print out the result by doing:

orgs.map(org => 
  f(org)
    .then(res => console.log(res)))

Any ideas on how this behavior happens?

Also I am using find-rss package over an array of links

What's the point of this function? To fill the space on screen? res => return res --- And no, it still is a promise. That function does nothing. You need to read some of those numerous blog posts about promises. -- "Still, this won't work." -- Of course it doesn't, you collect promises. Just read up on what promises are and how they work. Reading documentation (includes blog posts) goes a long way towards solving soooo many problems. This is not a question worth sharing and archiving on SO. — Mörre
– Mörre, Commented Dec 15, 2017 at 6:33

ryanlee · Accepted Answer · 2017-12-15 06:42:12Z

1

you can use Promise.all() to aggregate the results of multiple promises. Promise is very useful is javascript.

var p1 = Promise.resolve(3);
var p2 = 1337;
var p3 = new Promise((resolve, reject) => {
  setTimeout(resolve, 100, 'foo');
}); 

Promise.all([p1, p2, p3]).then(values => { 
  console.log(values); // [3, 1337, "foo"] 
});

this is a simple example, as u known, your orgs map result is an promise array, so you can use Promise.all to get what u want

answered Dec 15, 2017 at 6:42

ryanlee

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