Promise.any

promise_any.js

// Promises are started in parallel.
// Resolves with the first resolved value in time. 
// If there's no winner, it rejects with last rejection.
Promise.any = function (promises) {
  return new Promise((resolve, reject) => {
    var rejectedCount = 0;
    function onMemberResolved(value) {
      resolve(value);
    }
    function onMemberRejected(reason) {
      if (++rejectedCount == promises.length)
        reject(reason);
    }
    function observeSettled(promise) { 
      promise.then(onMemberResolved)
             .catch(onMemberRejected);
    }
    promises.forEach(observeSettled);
  });
};
Promise.fastest = Promise.any;