A wrapper around promises that allows for easy chaining them together.

PromiseChain.ts

/**
 * Created by Dimitris Vlachakis (TheCrafter) on 23/10/2019
 * https://github.com/TheCrafter
 * https://gist.github.com/TheCrafter/eb32496eaa050e0fa616705789c4df6c
 *
 * A wrapper around promises that allows for easy chaining them together.
 *
 * Example usage:
 * {code}
 * const pc = new PromiseChain<number>(125);
 * pc.append(async (n) => { log(n); return n + 5; })
 * pc.append(async (n) => { log(n); throw ("wtf"); })
 * pc.append(async (n) => { log(n); return n + 5; })
 * pc.append(async (n) => { log(n); return n; });
 * try {
 *  await pc.wait();
 * } catch (e) {
 *   log(e);
 * }
 * {/code}
 */
export default class PromiseChain<State> {
  private _promise: Promise<State> = Promise.resolve({} as State);

  constructor(s: State) {
    this.reset(s);
  }

  public reset(s: State = {} as State) {
    this._promise = Promise.resolve(s);
  }

  public append(f: (s: State, ...args: any[]) => Promise<State>, ...args: any[]) {
    this._promise = this._promise.then(async (s :State) => {
      return await f(s, ...args);
    })
  }

  public async wait() {
    try       { await this._promise; }
    catch (e) { throw e;             }
    finally   { this.reset();        }
  }
}