Future: Асинхронность на фьючерах без состояния

future.js

// © Timur Shemsedinov
// https://www.youtube.com/watch?v=22ONv3AGXdk
// https://github.com/HowProgrammingWorks/Future

class Future {
  constructor(executor) {
    this.executor = executor;
  }

  static of(value) {
    return new Future(resolve => resolve(value));
  }

  chain(fn) {
    return new Future((resolve, reject) => this.fork(
      value => fn(value).fork(resolve, reject),
      error => reject(error),
    ));
  }

  map(fn) {
    return this.chain(value => Future.of(fn(value)));
  }

  fork(successed, failed) {
    this.executor(successed, failed);
  }

  promise() {
    return new Promise((resolve, reject) => {
      this.fork(
        value => resolve(value),
        error => reject(error),
      );
    });
  }
}

const futurify = fn => (...args) => new Future((resolve, reject) => {
  fn(...args, (err, data) => {
    if (err) reject(err);
    else resolve(data);
  });
});