Deferred Promises, a useful tidbit that jQuery devised

deferredpromise.js

export class DeferredPromise {
  // A definition of this.resolve. If null, this object is uninitialized
  resolve = null;
  
  // A definition of this.reject. If null, this object is uninitialized
  reject = null;
  
  // A definition of this.promise. If null, this object is uninitialized
  promise = null;
  
  // Creates a new instance of DeferredPromise, optionally auto resolving
  // or rejecting a value. If both are supplied, a truthy autoResolve value
  // will be resolved and otherwise the autoReject value will be reject()'ed
  //
  // @param {any} autoResolveValue a value to automatically resolve
  // @param {any} autoRejectedValue a value to automatically reject
  constructor(autoResolvedValue, autoRejectedValue) {
    this.promise = new Promise((resolve, reject) => {
      Object.assign(this, { resolve, reject });
      
      if (autoResolvedValue) {
        resolve(autoResolvedValue);
      }
      else if (autoRejectedValue) {
        reject(autoRejectedValue);
      }
    });
  }
  
  // Ensures any usage of this instance in Object.toString.prototype will produce
  // a string indicating "[object DeferredPromise]" for ease of identification
  get [Symbol.toStringTag]() { return this.constructor.name }
}

export function applySideEffects() {
  Promise.prototype.deferred = function() {
    return new DeferredPromise(...arguments);
  }
}

export function Deferred() {
  return new DeferredPromise(...arguments);
}

Also as a one liner

const Deferred = () => { let o = {}; o.promise = new Promise((resolve, reject) => Object.assign(o, { resolve, reject })); return o; }