use deferreds

Defer.js

class Defer {
  constructor() {
    this.promise = new Promise((resolve, reject) => 
      Object.assign(this, {resolve, reject})
    );
  }
}

Defer.ts

export class Defer<T> {
  promise: Promise<T>;
  resolve: (value: T | PromiseLike<T>) => void = () => {};
  reject: (reason?: unknown) => void = () => {};

  constructor() {
    this.promise = new Promise<T>((resolve, reject) => {
      this.resolve = resolve;
      this.reject = reject;
    });
  }
}