Opinions on externally controlled promises?

It's become a convenient pattern on my team to store resolve functions on an external object when coordinating some async work. Does anyone else use promises like this? Maybe there are some unforeseen pitfalls?

For instance, let's say we're loading images and doing some canvas draws with them.

class CatPichurs {
  constructor() {
    // promise control
    this.cats = {
      felix: {
        promise: new Promise(resolve => this.resolveFelix = resolve)
      },
      cheshire: {
        promise: new Promise(resolve => this.resolveCheshire = resolve)
      },
      garfield: {
        promise: new Promise(resolve => this.resolveGarfield = resolve)
      }
    }

    Promise.all([
      this.cats.felix.promise, 
      this.cats.cheshire.promise, 
      this.cats.garfield.promise
    ])
    .then(allTheCats => {
      allTheCats.forEach(cat => {
        // some big reveal logic
      })
    });
  }

}

class ExternalImageMagic {
  constructor(cats) {
    let felix, cheshire, garfield;

    // load some pictures and draw
    cats.resolveFelix(felix);

    // load more pictures and draw
    cats.resolveCheshire(cheshire);

    // and a couple of Garfield to draw
    cats.resolveGarfield(garfield);
  }
}

const someCats = new CatPichurs();
const imageStuff = new ExternalImageMagic(someCats);

While this example makes no sense, you can see how this pattern is handy for keeping the cat rendering in one place and the image manipulation in another while ensuring both of them are coordinated.

What does the dev community think?

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Opinions on externally controlled promises?

Harry Dennen

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