An idea for promise cancelation (it doesn’t really cancel the promise, just make sure it never resolves or rejects)

make-cancelable.js

// Just an idea, completely untested!
function makeCancelable(promise) {
    let canceled = false;
    const proxy = new Promise((resolve, reject) => {
        promise.then(
            (value) => canceled === false && resolve(value), 
            (error) => canceled === false && reject(error)
        );
    });

    proxy.cancel = () => canceled = true;
    return proxy;
}