Deferred promise

deferred_promise.js

class DeferredPromise extends Promise {

  constructor(def = (res, rej)=>{}) {
    let res, rej;
    super((resolve, reject)=>{
      def(resolve, reject);
      res = resolve;
      rej = reject;
    });
    this.resolve = res;
    this.reject = rej;
    this.isCancelled = false;
  }

  cancel(err) {
    this.isCancelled = true;
    this.reject(err || new Error("Cancelled deferred promise."));
  }

  defer(task) {
    this.task = task;
  }

  async execute(...args) {
    if (!this.task) {
      return this.reject(new Error("No task defined in deferred promise."));
    }
    try {
      args.push(this);
      const value = await this.task.call(this, ...args);
      this.resolve(value);
    } catch(err) {
      this.reject(err);
    }
  }

}

module.exports = DeferredPromise;

Wow, this is really close to what I came up with, but yours actually works 😂
However, I cannot understand why 🤔 Would you mind explaining why adding the def parameter to the constructor and calling it from within that function supplied to super actually works? 🙏

I believe, because I can't exactly remember, that the await keyword needs it, for some reason, perhaps transpiling through Babel requires it?

The easiest thing to do is to remove line 6 and the constructor default and see what happens.

I did once know but it was a while ago. Apologies.

I totally understand, thanks for you time 🙏