Wait until all promises complete even if some rejected

Question

Let\'s say I have a set of Promises that are making network requests, of which one will fail:

// http://does-not-exist will throw a TypeError
va         


        

Answer 1

Here's my custom settledPromiseAll()

const settledPromiseAll = function(promisesArray) {
  var savedError;

  const saveFirstError = function(error) {
    if (!savedError) savedError = error;
  };
  const handleErrors = function(value) {
    return Promise.resolve(value).catch(saveFirstError);
  };
  const allSettled = Promise.all(promisesArray.map(handleErrors));

  return allSettled.then(function(resolvedPromises) {
    if (savedError) throw savedError;
    return resolvedPromises;
  });
};

Compared to Promise.all

• If all promises are resolved, it performs exactly as the standard one.

• If one of more promises are rejected, it returns the first one rejected much the same as the standard one but unlike it waits for all promises to resolve/reject.

For the brave we could change Promise.all():

(function() {
  var stdAll = Promise.all;

  Promise.all = function(values, wait) {
    if(!wait)
      return stdAll.call(Promise, values);

    return settledPromiseAll(values);
  }
})();

CAREFUL. In general we never change built-ins, as it might break other unrelated JS libraries or clash with future changes to JS standards.

My settledPromiseall is backward compatible with Promise.all and extends its functionality.

People who are developing standards -- why not include this to a new Promise standard?