Ember cancellable promise

cancellable-promise.js

import Ember from 'ember';

export class CancellablePromise extends Ember.RSVP.Promise {
  constructor(resolver, cancel, label) {
    super(function (resolve, reject) {
      try {
        resolver(function resolved(value) {
          cleanup();
          resolve(value);
        }, function rejected(reason) {
          cleanup();
          reject(reason);
        });
      } catch (e) {
        cleanup();
        reject(e);
      }
    }, label);

    function cleanup() {
      delete self._cancel;
    }

    let self = this;
    this._cancel = cancel;
  }

  cancel() {
    if (this._cancel) {
      this._cancel();
      delete this._cancel;
    }
  }

  then() {
    let parent = this;
    let child = super.then(...arguments);
    // cancellation travels upstream to parent promises
    child._cancel = () => parent.cancel();
    return child;
  }
}