cancellable promise top on `Promise` @ https://github.com/azu/promises-book/issues/6

cancellable-promise-test.js

/**
 * Created by azu on 2014/05/02.
 * LICENSE : MIT
 */
"use strict";
var CancellablePromise = require("../src/cancellable-promise");
describe("CancellablePromise", function () {
    it("is cancellable promise", function (done) {
        var promise = new CancellablePromise(function (resolve, reject) {
            setTimeout(function () {
                reject(new Error("reason is reasonable"));
            }, 1000);
        });
        promise.onCancel(function (reason) {
            console.log("2. main canceled", reason);
            done();
        });
        var result = promise.then(function (value) {
            console.log(value);
        }).catch(function (error) {
            console.error("-", error);
            done();
        });
        result.onCancel(function () {
            console.log("1. result canceled");
        });
        result.cancel("Da!");
    });
});

cancellable-promise.js

/**
 * Created by azu on 2014/05/02.
 * LICENSE : MIT
 */
"use strict";
var CancellablePromise = function (executor) {
    this._canceld = false;
    Promise.call(this, executor);
};
if (typeof Object.setPrototypeOf === "function") {
    Object.setPrototypeOf(CancellablePromise, Promise);
} else {
    CancellablePromise.__proto__ = Promise;
}

CancellablePromise.prototype = Object.create(Promise.prototype, {
    constructor: {
        value: CancellablePromise
    }
});
CancellablePromise.prototype.cancel = function (reason) {
    var targetPromise = this;
    do {
        targetPromise._canceld = true;
        if (targetPromise._callback) {
            targetPromise._callback.call(targetPromise, reason);
        }
    } while (targetPromise = targetPromise._parentPromise);
};

CancellablePromise.prototype.isCanceled = function () {
    return this._canceld;
};
CancellablePromise.prototype.onCancel = function (fn) {
    this._callback = fn;
};
CancellablePromise.prototype.then = function passCatch(onFulfilled, onRejected) {
    var that = this;
    var promise = Promise.prototype.then.call(that, function (value) {
        if (!that.isCanceled()) {
            onFulfilled.call(that, value);
        }
    }, function (reason) {
        if (!that.isCanceled()) {
            onRejected.call(that, reason);
        }
    });
    promise._parentPromise = this;
    return promise;
};
module.exports = CancellablePromise;