CancellablePromise.js

const noop = () => {};

export default class CancellablePromise {
    constructor(executorOrPromise){
        this._promise = new Promise((resolve, reject) => {
            let promise = executorOrPromise;
            if(!promise.then) promise = new Promise(executorOrPromise);

            promise.then((...args) => {
                if(this.cancelled) reject('cancelled', ...args);
                else resolve(...args);
            });

            promise.catch(reject);
        });
    }

    cancel() {
        this.cancelled = true;
        this.catch(noop);
        return this;
    }

    then(func) {
        return new CancellablePromise(this._promise.then(func));
    }

    catch(func) {
        return new CancellablePromise(this._promise.catch(func));
    }
}