Lazier Functional Promise

lazy_functional_promise.js

/**
 * Functional promise
 */
var Promise = (function createPromise(listeners, resolved) {
    var self = this;

    if (typeof listeners === 'undefined') {
        listeners = [];
    }

    function resolve() {
        var args = Array.prototype.slice.call(arguments, 0);
        listeners.forEach(function (fn) {
            fn.apply(this, args);
        })
        return createPromise([], args);
    }

    resolve.done = function () {
        return function (fn) {
            if (typeof resolved !== 'undefined') {
                fn.apply(this, resolved);
                return self;
            }
            return createPromise(listeners.concat([fn]));
        };
    };

    return resolve;
}());

/**
 * Do manad
 */
function doMonad() {
    var args = arguments;
    return function () {
        Array.prototype.reduceRight.call(args, function (prev, curr) {
            if (typeof prev === 'undefined') {
                return curr;
            } else {
                return curr(prev);
            }
        });
    };
}

/**
 * Testing side effect free asyncronous function with a monad
 */
function getUsers() {
    return function (resolve) {
        setTimeout(function () {
            resolve('Hello, world!');
        }, 1000);
    };
}

doMonad(
    getUsers(),
    Promise.done(),
    function (data) {
        console.log('Data!!!!', data);
    }
)();