How do you implement a “raceToSuccess” helper, given a list of promises?

Question

I\'m puzzled by something in the ES6 Promise API. I can see a clear use case for submitting multiple async jobs concurrently, and \"resolving\" on the first success. This wo

Answer 1

Is there something in the API that permits a "raceToSuccess" kind of behavior

Soon, there almost certainly will be. There is a Stage 3 proposal for Promise.any:

Promise.any() takes an iterable of Promise objects and, as soon as one of the promises in the iterable fulfills, returns a single promise that resolves with the value from that promise.

So, the following syntax will be valid:

// assume getApi returns a Promise

const promises = [
  getApi('url1'),
  getApi('url2'),
  getApi('url3'),
  getApi('url4'),
];
Promise.any(promises)
  .then((result) => {
    // result will contain the resolve value of the first Promise to resolve
  })
  .catch((err) => {
    // Every Promise rejected
  });

Promise.any has been implemented in Spidermonkey, and there are some polyfills available.