Functional Promise

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

    return resolve;
}());

/**
 * Do manad
 */
function doMonad() {
    Array.prototype.reduceRight.call(arguments, 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);
    }).done(function (data) {
        console.log('Foo', data);
    })
);