eventwaiter.js

class EventWaiter {

  _emitter: EventEmitter;
  _event: string;
  _promise: Promise<mixed>;
  _accept: Function;

  _onEvent = (value) => {
    this._accept(value);
    this._emitter.removeEventListener(this._event, this._onEvent);
  };

  constructor(emitter: EventEmitter, event: string) {
    this._emitter = emitter;
    this._event = event;

    this._promise = new Promise((accept) => {
      this._accept = accept;
      emitter.on(event, this._onEvent);
    });
  }

  await(): Promise {
    return this._promise;
  }

  release() {
    this._emitter.removeEventListener(this._event, this._onEvent);
    this._accept();
  }
}