Simple Cancelable Promise

cancelablePromise.js

/*
 * A Promise which can be "cancelled".
 * This is not related to https://github.com/promises-aplus/cancellation-spec/issues.
 *
 * I just needed some mechanism to force-reject an on-going promise, and possibly execute a callback on cancellation.
 * Hope this example helps someone!
 */
function CancelablePromise(executor, onCancel) {
    var cancelFunc;
    var cancelable = new Promise(function(resolve, reject) {
        cancelFunc = reject;
    });
    var instance = Promise.race([new Promise(executor), cancelable]);
    instance.cancel = function() {
    	cancelFunc();
      	typeof onCancel === 'function' && onCancel();
    };    
    return instance;
}