Javascript promises demo

gistfile1.js

/**
 * Check out following URL's
 * http://www.html5rocks.com/en/tutorials/es6/promises/
 * http://www.html5rocks.com/en/tutorials/es6/promises/#toc-async
 * http://blog.parse.com/2013/01/29/whats-so-great-about-javascript-promises/
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
 * 
 * Try this code out on http://repl.it/
 * 
 * At present, promises are not yet supported by all browsers and some javascript libraries 
 * offer this functionality already.
 * 
 * Q seems to be a popular implementation but it's performance seems not that good
 * https://github.com/kriskowal/q
 * 
 * Bleubird seems like the most promising implementation in terms of performance
 * https://github.com/petkaantonov/bluebird
 * 
 * I hope to find some time soon to prepare a demo with bluebird.
 ***/

function factorial(n) {
    return new Promise(function(resolve, reject) {
        if (n < 0) {
            reject(new Error("n has to be larger than 0!!"));
        } else {
            var result = 1;
            do {
                result *= n;
                n--;
            }
            while (n > 1);
            return resolve(result);            
        }
    });

}    


function onSucces(result) {
    console.log("succesfully calculated " + result);
}

function onError(error) {
    console.log(error.toString());
}

factorial(5).then(onSucces, onError);
//succesfully calculated 120


factorial(-3).then(onSucces, onError);
//Error: n has to be larger than 0!!