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Cancellable Promises

mckabue profile image Kabue Charles ・1 min read

I want to be able to cancel my promises, and am using something inspired by:

const makeCancelable = promise => {
    let rejectFn;

    const wrappedPromise = new Promise((resolve, reject) => {
        rejectFn = reject;

        Promise.resolve(promise)
            .then(resolve)
            .catch(reject);
    });

    wrappedPromise.cancel = () => {
        rejectFn({ canceled: true });
    };

    return wrappedPromise;
};

Usage:

const cancelablePromise = makeCancelable(myPromise);
// ...
cancelablePromise.cancel();

The solution above works, but i would like to improve it and am not willing to use bluebirdjs or Observables (well, at least not currently...)

I would want to have that as a prototype of the Promise object, so i could call cancel on any native promise.

Anyone willing to offer the simplest implementation direction?

Discussion

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bradtaniguchi profile image
Brad

First does the example work?

Second, what would you want to improve if it works?

Third, if it doesn't work, whats wrong with using the mentioned libraries instead? Yes we all use too many libraries, but there is always the argument of not re-inventing the wheel right?

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paul_melero profile image
Paul Melero

I would advise you against adding properties to native prototypes. As it can lead to prototype names clashes. Adding options to native prototypes is like creating global variables, but worse. ;P

See what Eric Elliot says about it:

github.com/ericelliott/speculation...

Also, you might want to check that library ;)

Aaand this one: npmjs.com/package/p-cancelable

Is the one that got uses underneath.