promise.any()

[vitaly-t]

I've been using promise in my every project, including this one: pg-promise, until I ran into the necessity of using promise.any() logic in my test cases, so I had to use Bluebird for testing, while keeping Promise for the production, which is awkward.

And now that I find I need promise.any in more than one case, it is becoming unfortunate that I have to move to Bluebird completely.

Please, add promise.any, it is a very important promise function!

[ForbesLindesay]

It's not a very commonly used promise function, and it's non-standard, so I'm not sure I want to add it to the core library.

It would not be too difficult to implement as a separate library, something like:

function promiseAny(promises) {
  if (!Array.isArray(promises)) return Promise.reject(new TypeError('promises must be an array'));
  if (promises.length === 0) return Promise.reject(new TypeError('Cannot call any on array of length 0'));
  return new Promise(function (resolve, reject) {
    var fulfilled = false, rejections = [];
    function onFulfill(result) {
      fulfilled = true;
      resolve(result);
    }
    function onReject(err) {
      if (fulfilled) return;
      rejections.push(err);
      if (rejections.length === promises.length) {
        // TODO: implement AggregateError
        reject(new AggregateError(rejections));
      }
    }
    promises.forEach(function (promise) {
      promise.then(onFulfill, onReject);
    });
  });
}

I think given how bluebird is currently about the only library to implement this and I've never had need of it myself, I'm not inclined to add it to the promise library.

[vitaly-t]

@ForbesLindesay Perhaps you are not doing any development that requires logical search patterns, because the pattern where one successful attempt in a set indicates overall success is in fact a very common one.

[edef1c]

@ForbesLindesay How does this differ from Promise#race, which does appear to be part of ES6?

[ForbesLindesay]

Consider:

var rejected = Promise.reject(new Error('Whatever'));
var fulfilled = new Promise(function (resolve) {
  setTimeout(() => resolve('success'), 500);
});

var any = Promise.any([rejected, fulfilled]);
// => fulfilled with 'success' after 500ms

var race = Promise.race([rejected, fulfilled]);
// => immediately rejected with `new Error('Whatever')`