promissary v0.2.0

Promisssary

A library for manually resolving promises.

Why?

I needed callbacks, but I didn't want to end up in a callback hell. I like Promises and this is what I wanted.

new SomeTask(<params>).run().then(val => (...));
// or
const val = await new SomeTask(<params>).run();

Q: ES6 Promises work. Why would anybody want to resolve them manually?

A: When using requestAnimationFrame, setTimeout or such you just don't have enough control to put everything in the Promise constructor. Well, you can of course, but I ended up with a messy code. So I built a wrapper around Promises to resolve them manually for this extra bit of flexibility.

Usage

import Promissary from 'promissary';

For the love of god, please define a promissary as private. You don't want anybody outside of your task to resolve it, do you?

class SomeTask {
  private finished: Promissary<boolean>;
  ...
}

Initialize it in a public method or a constructor

  constructor() {
    ...
    this.finished = new Promissary<boolean>();
    ...
  }

Do the actual asynchronous part in a private method and resolve.

  private doTheWork() {
    ...
    // however you're gonna check if it is done
    if (this.done()) {
      this.finished.resolve(true);
    }

    // as an example of why you might want to need to resolve the promise manually
    requestAnimationFrame(doTheWork.bind(this));
  }

Make a public method returning the promise

  public run() {
    this.doTheWork();
    return this.finished.promise;
  }

Now you can execute your asynchronous task with then or await.

Typescript

It's written in typescript and the type definitions are included. Tbh, I don't think it's a good idea to use this in vanilla javascript. At least the typescript compiler does enforce private functions.