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

• Mörre: 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.

Answer 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