I like q.js's spread idea to an ordered argument list instead of an array of results

Spread Promise.all

(function (Promise:Function /* Strange, but true... according to Flow */) {
  "use strict"
  
  // This function cannot(!) use the 'this'-binding fat arroq: () ==> {}
  Promise.spread = function (promises:Array, fulfilled:Function, rejected:?Function):Promise {
    return Promise.all(promises).spread(fulfilled, rejected)
  }

  // This function cannot(!) use the 'this'-binding fat arroq: () ==> {}
  // eslint-disable-next-line no-extend-native
  Promise.prototype.spread = function (fulfilled:Function, rejected:?Function):Promise {
    return this.then((allResults:Array):Promise => {
      return fulfilled(...allResults)
    }, rejected)
  }
})(Promise)