node-downloaderJS using coroutines and generators

download.js

/* This is just a cool example on how to write coros in javascript Ecma6.
* Licence: MIT
* Author: esteban castro borsani
*/
    
    var http = require('http');
    var fs = require('fs');
    var path = require('path');
    var Q = require("q");
    var co = require("co");

    function request(opts) {
        var deferred = Q.defer();

        http.request(opts, deferred.resolve)
            .on('error', deferred.reject)
            .end();

        return deferred.promise;
    }

    function pipe(readable, writtable, progressUpdate) {
        var deferred = Q.defer();

        function ondata(){
            progressUpdate(writtable.bytesWritten);
        }

        function onfinish(){
            progressUpdate(writtable.bytesWritten);
            deferred.resolve();
        }

        readable.on('data', ondata)
            .on('error', deferred.reject);

        writtable.on('error', deferred.reject)
            .on('finish', onfinish);

        readable.pipe(writtable);

        return deferred.promise;
    }

    function update(bytesWritten) {
        // show progress somewhere
    }

    function* downloadCoro() {
        var execPath = path.dirname(process.execPath);
        var destPath = execPath + "/downloads/out";
        var file = fs.createWriteStream(destPath, {flags: 'w', encoding: null});

        try {
            var res = yield request({host: "releases.ubuntu.com", path: "/14.04.1/ubuntu-14.04.1-desktop-amd64.iso"});
            yield pipe(res, file, update);
        } catch (err) {
            console.error(err.stack);
        }
    }

    var download = coWrapper(downloadCoro);

    function coWrapper(coro){
        return function (){
            co(coro).catch(onerror);
        }
    }

    function onerror (err) {
        console.error(err.stack);
    }