Y.CancellablePromise

cancellable_promise.js

/**
 * Error used as a rejection reason for canceled Promises.
 *
 * @class Promise.CancellationError
 * @constructor
 * @extends {Error}
 * @param {String} opt_message An optional debugging message for describing the
 *     cancellation reason.
 */
function CancellationError(opt_message) {
    CancellationError.superclass.constructor.apply(this, arguments);
    this.message = opt_message;
}

A.extend(CancellationError, Error, {
    name: 'cancel'
});

A.Promise.CancellationError = CancellationError;

/**
 * Cancellable promise.
 *
 * @class CancellablePromise
 * @constructor
 * @extends {Promise}
 * @param {Function} fn A function where to insert the logic that resolves this
 *     promise. Receives `fulfill` and `reject` functions as parameters. This
 *     function is called synchronously.
 */
function CancellablePromise() {
    CancellablePromise.superclass.constructor.apply(this, arguments);
}

A.extend(CancellablePromise, A.Promise, {
    then: function() {
        var instance = this,
            promise = CancellablePromise.superclass.then.apply(this, arguments);
        promise.cancel = A.bind(instance.cancel, instance);
        return promise;
    },

    cancel: function(opt_message) {
        this._resolver.reject(new A.Promise.CancellationError(opt_message));
    }
});

A.CancellablePromise = CancellablePromise;