Using promises and reactive programming (RxJs) to implement asynchronous pagination

reactive-promises-paginations.js

const Rx = require('rx');

getPages(5, 1)
    .then(reduceToPromise)
    .then(console.log)

function getPages(perPage, page) {
    return new Promise(function(resolve, reject) {
        resolve(getAllPages(perPage, page));
    });
}

function getAllPages(perPage, page) {
    return Rx.Observable.fromPromise(getPage(perPage, page))
        .flatMap((data) => {
            const items = Rx.Observable.fromArray(data.Data);
            const next = data.Data.length === perPage ? // whatever condition works
                getAllPages(perPage, page + 1) :
                Rx.Observable.empty();

            return Rx.Observable.concat(
                items,
                next
            );
        });
}

function getPage(perPage, page) {
    const content = page < 3 ? [1, 2, 3, 4, 5] : [];

    return Promise.resolve({
        Data: content
    });
}

// Accumulates the results and return them as a promise so you can chain after it
function reduceToPromise(observable) {
    function accumulate(acc, item) {
        acc.push(item);
        return acc;
    }

    return observable.reduce(accumulate, []).toPromise();
}