Extend promise with extra data

Question

I'm using kriskowal/q promise library to handle http requests, but to simplify the case, let's assume I have an array of promises created dynamically and pushed to the promises array:

var promises = [],
    ids = ['foo', 'bar', 'buz'];

ids.forEach(function(id){
  var promise = Q.fcall(function () {
    return 'greetings with ' + id;
  });

  promises.push(promise);
});

// and handle all of them together:
Q.all(promises).then(function (results) {
  console.log(results);
});

// gives:
[ 'greetings with foo',
  'greetings with bar',
  'greetings with buz' ]

The question is - is it possible to assign somehow an id to the promise to obtain it later in all execution ?

Let's assume that we cannot modify the returned value (it comes from the API and I cannot extend it with extra data).

`Promise.all` [guarantees the order of results](http://stackoverflow.com/a/28066851/2806996), so can you use the index of each element in `results` to look up the id (trivially in your example)? — joews, Oct 30 '15 at 11:39
Now with correct link - my comment referred to ES6 `Promise.all`, but `Q.all` makes the same guarantee. — joews, Oct 30 '15 at 11:46

score 1 · Accepted Answer · edited Oct 30 '15 at 11:45

1

Q.all guarantees result order, so you can use the index of each element in results to look up the id. In your example:

Q.all(promises).then(function (results) {
  results.forEach(function(results, i) {
    var id = ids[i];
  })
});

edited Oct 30 '15 at 11:45

hsz

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answered Oct 30 '15 at 11:45

joews

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Extend promise with extra data

1 Answers1