cancelable promise

cancelable-promise.js

/**
 * @file cancelable promise
 */
const pending = Promise.race.bind(Promise, []);
export default function cancellablePromise(fn) {
    let isPending = true;
    const patch = fn => (...args) => {
        isPending = false;
        if (fn) {
            fn(...args);
        }
    };
    return new Promise((fulfill, reject) => {
        const cancel = () => {
            if (isPending) {
                fulfill(pending());
            }  
        };

        fn(patch(fulfill), patch(reject), cancel);
    });
}