promise.js

var guid = 0;

function getGuid() {
    guid += 1;
    var id = guid;
    console.log('Generated guid', id);
    return new Promise(resolve => {
        setTimeout(() => {
          resolve(id);
        }, (Math.random() * 1.5 | 0) * 1000);
    });
}

Promise.map = function(collection, method) {
    return Promise.all(collection.map(method));
}

Promise.series = function(methods) {
    var promise = Promise.resolve();

    return Promise.all(methods.map(method => {
        return promise = promise.then(method);
    }));
}

Promise.mapSeries = function(collection, method) {
    return Promise.series(collection.map(item => {
        return () => {
            return method(item);
        };
    }));
}


Promise.resolve().then(function() {

    // In parallel

    return Promise.map(Array.from({length: 10}), getGuid)
        .then(function(result) {
            console.log(result)
        });

}).then(function() {

    // In series

    return Promise.mapSeries(Array.from({length: 10}), getGuid)
        .then(function(result) {
            console.log(result)
        });
});